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A1 verb #3,000 most common 7 min read

mordre

Top 3,000

Practice it Examples Notes & Tips mordre in 30 Seconds

Explanation mordre in your Level:

At the A1 level, 'mordre' is taught as a basic physical action. Students learn it primarily in the context of animals (the dog bites) or simple eating actions. The focus is on the present tense: 'Je mords', 'Tu mords', 'Il mord'. It is important for beginners to distinguish 'mordre' from 'manger' (to eat). While 'manger' covers the whole process, 'mordre' is just the initial act of the teeth. Learners should also be introduced to the warning 'Attention, il mord!' as a safety phrase. Simple sentences like 'Le chat ne mord pas' are typical at this stage.

At A2, the usage expands to include the past tense (Passé Composé: 'Il a mordu') and the reflexive form 'se mordre'. Learners start to talk about minor accidents, such as 'Je me suis mordu la langue' (I bit my tongue). This level also introduces the preposition 'dans' for biting into food. Students should begin to understand that 'mordre' is for teeth, while 'piquer' is for insects. The concept of 'mordre' in sports, specifically 'mordre la ligne' (stepping over the line), is also introduced in the context of hobbies and physical activities.

At the B1 level, learners encounter 'mordre' in more idiomatic and abstract contexts. The most common idiom introduced is 's'en mordre les doigts' (to regret something). This level requires understanding the emotional weight of the verb. 'Mordre à l'hameçon' (to take the bait) is also common here, often used in stories or news reports about scams or tricks. Learners should be comfortable using 'mordre' in various tenses, including the Imparfait and the Futur Simple, to describe ongoing habits or future consequences.

B2 learners explore the metaphorical 'mordre sur'. This involves encroachment, such as 'le travail mord sur ma vie privée' (work is encroaching on my private life). The nuance here is that the encroachment is often unwanted. This level also introduces the adjective 'mordant' (biting/incisive), used to describe a person's wit, a cold wind, or a critical review. Students are expected to use 'mordre' to express complex ideas about boundaries and critical thinking in debates or essays.

At C1, 'mordre' is used in sophisticated literary and technical contexts. It might describe how a chemical 'bites' into a surface (corrosion) or how a philosopher 'mord' into a complex problem. The register shifts toward the academic and the precise. Learners should understand subtle differences between 'mordre', 'ronger', and 'entamer'. They also explore historical or rare idioms like 'mordre la poussière' (to bite the dust) in literature and formal speeches, recognizing the stylistic impact of such choices.

For C2 speakers, 'mordre' becomes a tool for stylistic mastery. It is used to analyze the 'mordant' of a text—the sharp, piercing quality of its argument. C2 learners use the verb to discuss the limits of language and physical reality, such as how an idea 'mord' (takes hold) in the public consciousness. They can navigate between the visceral physical meaning and the highly abstract metaphorical meanings with ease, using the verb to add flavor and intensity to their high-level discourse.

Practice it Examples Notes & Tips

mordre in 30 Seconds

Mordre means 'to bite' physically or metaphorically.
It is a regular -re verb in the third group.
It requires 'dans' when biting into food.
Common idioms involve regret and taking bait.

The French verb mordre primarily translates to 'to bite' in English. At its most basic level, it describes the action of using teeth to cut, grip, or pierce something. However, in the rich tapestry of the French language, its utility extends far beyond the simple act of mastication or a defensive animal reflex. Understanding mordre requires looking at it through several lenses: the physical, the metaphorical, and the idiomatic.

The Physical Act: In everyday life, you will use this verb to describe eating hard foods, like biting into an apple (mordre dans une pomme), or to describe the behavior of animals. It is a transitive verb, meaning it usually takes a direct object.

Fais attention, le petit chien pourrait te mordre si tu lui prends son jouet.

Beyond the physical, mordre is used to describe how one thing encroaches upon another. In technical or architectural contexts, you might hear about a building 'biting' into the sidewalk (mordre sur le trottoir). This sense of encroachment is vital for intermediate learners to grasp, as it shifts the verb from a biological action to a spatial one.

Metaphorical Enthusiasm: In a more abstract sense, 'mordre' describes an interest or lack thereof. If you 'mordez à' a subject, it means you have taken the bait or become deeply interested. Conversely, if a student 'ne mord pas' to a lesson, they are not engaging with it.

Elle a tout de suite mordu à l'idée de partir en voyage humanitaire.

Finally, the verb appears in numerous common expressions that define the French temperament, such as 's'en mordre les doigts' (to regret something bitterly). This breadth makes mordre an essential A1 verb that evolves with you as you reach C2 proficiency.

Using mordre correctly involves understanding its conjugation and its relationship with prepositions. As a third-group verb ending in -re, it follows a relatively predictable pattern, though learners must be careful with the 'nous' and 'vous' forms where the 'd' is followed by the 'o' or 'e'.

Direct Object Usage: When you bite an object or a person directly, no preposition is needed. 'Le serpent mord sa proie' (The snake bites its prey). Here, the action is direct and immediate.

L'enfant a mordu son frère pendant la dispute.

However, when we talk about biting into something, French speakers favor the preposition 'dans'. This adds a layer of depth to the action, suggesting the teeth are entering the substance. 'Mordre dans la vie' (to bite into life) is a common way to express living with passion.

The Preposition 'À': The preposition 'à' is used when 'mordre' means 'to take the bait' or 'to react to a stimulus'. This is common in fishing (le poisson mord à l'hameçon) and in social manipulation.

Il est tellement naïf qu'il mord à toutes les plaisanteries.

In the reflexive form, se mordre, the verb often refers to biting one's own body parts, usually by accident. 'Je me suis mordu la langue' (I bit my tongue). This is a vital reflexive construction for talking about minor injuries or accidents during meals.

In contemporary French culture, mordre is heard in a variety of settings, ranging from the domestic to the professional. If you are in a park in Paris, you might hear a parent warning their child, 'Attention, le chien peut mordre!' This is the most literal and common auditory encounter with the word.

Sports and Games: In sports like long jump or sprinting, 'mordre la ligne' means to step over the line, resulting in a foul. Commentators will frequently shout 'Il a mordu!' when a jump is disqualified.

Le sauteur a malheureusement mordu de deux centimètres.

In the workplace, the word takes on a more abstract meaning regarding time management. 'Mordre sur le temps de pause' means to cut into or encroach upon break time. This is a common complaint among employees in France who value their 'temps libre'.

Literary and Journalistic Use: Journalists often use 'mordre' to describe a sharp, incisive critique. A 'style mordant' is a biting or sarcastic writing style that 'bites' into the subject matter with wit and severity.

Cet éditorialiste a un ton très mordant envers le gouvernement.

Finally, in the kitchen, you might hear 'mordre' when discussing the texture of food. If a vegetable is 'al dente', a French chef might describe it as having a bit of 'mordant' or 'sous la dent', though 'mordre' itself is usually reserved for the action of the eater.

Even though mordre seems straightforward, English speakers often stumble over its nuances and its conjugation. The first major hurdle is the confusion between 'mordre' and 'piquer'.

The 'Piquer' vs 'Mordre' Dilemma: In English, we say a mosquito 'bites'. In French, a mosquito 'pique' (stings/pricks). Using 'mordre' for an insect is a classic 'anglicisme'. You only 'mordre' if you have teeth!

Incorrect: Le moustique m'a mordu. Correct: Le moustique m'a piqué.

Another common mistake is the conjugation of the present tense. Many learners forget that the 'd' remains in the singular forms: je mords, tu mords, il mord. Beginners often try to treat it like a regular -er verb and say 'je morde', which is incorrect.

Preposition Errors: Learners often omit the 'dans' when talking about eating. Saying 'Je mords la pomme' is grammatically possible but sounds like you are attacking the apple. 'Je mords dans la pomme' sounds like you are enjoying a snack.

Il a mordu dans son pain avec appétit.

Lastly, the reflexive form 'se mordre' requires the definite article for body parts, not the possessive adjective. It is 'Je me mords la joue' (I bite my cheek), not 'Je mords ma joue'. This is a general rule for body parts in French that applies to 'mordre' as well.

To truly master mordre, you should know its synonyms and how they differ in intensity and context. French offers several verbs that describe tooth-related actions with more precision.

Grignoter vs Mordre: 'Grignoter' means to nibble or snack. While 'mordre' implies a firm grip or a cut, 'grignoter' is repetitive and light. You 'mordre' a steak, but you 'grignote' some nuts.

La souris grignote le fromage au lieu de le mordre franchement.

Another alternative is 'ronger', which means to gnaw or eat away at. 'Ronger' is used for rodents or for metaphorical things like worry ('rongé par l'inquiétude'). 'Mordre' is a single action, whereas 'ronger' is a process over time.

Déchiqueter: If the biting is violent and results in the object being torn apart, 'déchiqueter' (to shred/tear to pieces) is more appropriate. This is often used in descriptions of wild animal attacks.

Le loup a déchiqueté le vêtement de l'homme.

In a metaphorical context, instead of 'mordre à l'hameçon', you might use 'se faire avoir' (to be had/tricked) or 'tomber dans le panneau' (to fall into the trap). These are less descriptive but very common in spoken French.

How Formal Is It?

Fun Fact

The word 'remorse' (remords in French) literally means 'a biting back' of the conscience, coming from the same root.

Pronunciation Guide

UK /mɔʁdʁ/

US /mɔrdɹə/

Stress is on the first syllable 'mor-'.

Rhymes With

tordre ordre recordre

Common Errors

Pronouncing the 'e' at the end too strongly.
Using an English 'r' instead of the French uvular 'r'.
Confusing it with 'mort' (death), which is pronounced similarly but without the 'dr' sound.

Difficulty Rating

Reading 2/5

Easy to recognize in texts due to its similarity to 'morsel' or 'remorse'.

Writing 3/5

Conjugation of -re verbs can be tricky for beginners.

Speaking 2/5

Pronunciation is straightforward once the French 'r' is mastered.

Listening 2/5

Clear sound, though can be confused with 'mort' in fast speech.

What to Learn Next

Prerequisites

dent chien manger bouche mal

Learn Next

ronger grignoter piquer mâcher avaler

Advanced

corrosion incisif mordacité sarcastique empiéter

Grammar to Know

Third Group Verbs (-re)

Je mords, Nous mordons.

Reflexive Verbs with Body Parts

Je me mords la langue (not ma langue).

Preposition 'dans' for penetration

Mordre dans un fruit.

Passé Composé with Avoir

J'ai mordu.

Adjective formation from verbs

Un ton mordant.

Examples by Level

Le chien mord la balle.

The dog bites the ball.

Subject + Verb + Direct Object.

Il ne faut pas mordre.

One must not bite.

Infinitive after 'il faut'.

Je mords dans une pomme.

I bite into an apple.

Use 'dans' for biting into food.

Est-ce que ton chat mord ?

Does your cat bite?

Interrogative sentence.

Le bébé mord son jouet.

The baby bites his toy.

Present tense singular.

Les enfants ne mordent pas.

The children do not bite.

Negative plural form.

Attention, il mords !

Watch out, he bites!

Imperative-like warning.

Tu mords trop fort.

You are biting too hard.

Adverb 'fort' modifying the verb.

Je me suis mordu la langue.

I bit my tongue.

Reflexive 'se mordre' + definite article.

Le chien a mordu le facteur.

The dog bit the mailman.

Passé composé with 'avoir'.

Elle a mordu dans le gâteau.

She bit into the cake.

Preposition 'dans'.

N'aie pas peur, il ne va pas te mordre.

Don't be afraid, he won't bite you.

Futur proche with 'aller'.

Le sauteur a mordu la ligne.

The jumper stepped over the line.

Sporting context.

Pourquoi as-tu mordu ton stylo ?

Why did you bite your pen?

Interrogative in passé composé.

Le poisson a enfin mordu.

The fish finally bit.

Intransitive use in fishing.

Il s'est mordu la joue en mangeant.

He bit his cheek while eating.

Reflexive + gérondif.

Si tu refuses cette offre, tu vas t'en mordre les doigts.

If you refuse this offer, you will regret it.

Idiom: s'en mordre les doigts.

Il a mordu à l'hameçon tout de suite.

He took the bait immediately.

Idiom: mordre à l'hameçon.

Le froid commençait à mordre ses joues.

The cold was starting to bite his cheeks.

Metaphorical use for weather.

Elle mords la vie à pleines dents.

She lives life to the fullest.

Idiom: mordre à pleines dents.

Je ne mords pas du tout à son projet.

I'm not interested in his project at all.

Metaphorical: not 'biting' (interested).

L'acide a mordu la plaque de métal.

The acid bit into the metal plate.

Technical/Chemical use.

Il a mordu sur son temps de repos pour finir le travail.

He cut into his rest time to finish the work.

Preposition 'sur' for encroachment.

Le vent était mordant ce matin-là.

The wind was biting that morning.

Participial adjective 'mordant'.

Cette nouvelle réglementation mord sur nos libertés.

This new regulation encroaches on our freedoms.

Abstract encroachment.

Il s'en mords les doigts d'avoir vendu sa voiture.

He regrets selling his car bitterly.

Idiom with 'en'.

La critique était particulièrement mordante.

The review was particularly biting.

Adjective use for criticism.

Le cheval a mordu son frein pendant toute la course.

The horse champed at the bit throughout the race.

Literal and metaphorical idiom.

Ils ont mordu la poussière lors du dernier match.

They bit the dust during the last match.

Idiom: mordre la poussière.

Le jardin mord sur la forêt voisine.

The garden encroaches on the neighboring forest.

Spatial encroachment.

Elle a un humour mordant qui ne plaît pas à tout le monde.

She has a biting humor that doesn't please everyone.

Adjective describing personality.

Le chien a mordu au vif de la plaie.

The dog bit into the quick of the wound.

Idiom: mordre au vif.

L'auteur mord à belles dents dans les travers de la société.

The author sinks his teeth into society's flaws.

Literary metaphor.

Le remords le mordait sans cesse.

Remorse was constantly gnawing at him.

Personification of remorse.

Le graveur laisse l'acide mordre le cuivre.

The engraver lets the acid etch the copper.

Artistic technical term.

Il ne faut pas mordre sur le domaine d'autrui.

One must not encroach upon others' property.

Formal/Legal context.

Son discours était empreint d'une ironie mordante.

His speech was marked by a biting irony.

High-level description of tone.

Elle a mordu à l'appât avec une naïveté déconcertante.

She took the bait with disconcerting naivety.

Sophisticated idiom usage.

La mer mordait la falaise à chaque tempête.

The sea bit into the cliff with every storm.

Literary personification of nature.

Il a fallu mordre sur le budget de l'année prochaine.

We had to dip into next year's budget.

Metaphorical use in finance.

L'œuvre de Nietzsche mord sur la pensée contemporaine.

Nietzsche's work bites into contemporary thought.

Intellectual encroachment.

C'est un texte qui mord, qui dérange, qui bouscule.

It's a text that bites, that disturbs, that shakes things up.

Abstract verbal use.

La réalité finit toujours par nous mordre au talon.

Reality always ends up nipping at our heels.

Existential metaphor.

Il y a dans son style un mordant qui rappelle Swift.

There is a sharpness in his style that recalls Swift.

Noun use 'le mordant'.

Le froid mords-moi-le-nœud de cet hiver est insupportable.

The pathetic/annoying cold of this winter is unbearable.

Slang/Vulgar idiom.

Elle s'en mordra les doigts jusqu'au sang.

She will regret it until she bleeds (extremely).

Hyperbolic idiom.

Le néant semble mordre sur l'existence même.

Nothingness seems to encroach upon existence itself.

Metaphysical usage.

La passion l'a mordu au cœur.

Passion bit him in the heart.

Poetic usage.

Common Collocations

mordre dans une pomme

mordre la ligne

mordre à l'hameçon

mordre sur le temps

se mordre la langue

un froid à mordre

mordre la poussière

mordre à pleines dents

mordre au vif

mordre le trait

Common Phrases

Attention, il mord !

— A common warning about an aggressive animal.

Ne touche pas ce chien, attention il mord !

Mordre dans le vif

— To get to the heart of a matter or to cut into living tissue.

Le chirurgien doit mordre dans le vif.

Ne pas mordre

— To not be interested or not respond to a provocation.

J'ai essayé de le fâcher, mais il n'a pas mordu.

Mordre sur le voisin

— To encroach on a neighbor's property.

Sa haie mord sur le terrain du voisin.

S'en mordre les doigts

— To regret something very much.

Tu t'en mordras les doigts plus tard.

Mordre la main qui nourrit

— To turn against someone who helps you.

Il ne faut pas mordre la main qui vous nourrit.

Mordre à la grappe

— To believe a lie easily.

Il a mordu à la grappe sans hésiter.

Mordre le frein

— To be impatient or to endure something difficult.

Il mords son frein en attendant les résultats.

Mordre à l'appât

— To take the bait.

Le client a mordu à l'appât publicitaire.

Mordre sur la chaussée

— To drive partially off the road or over the line.

La voiture mord sur la chaussée opposée.

Often Confused With

mordre vs mort

Pronounced similarly, but 'mort' means death/dead.

mordre vs maure

A Moor (historical group), sounds identical in some accents.

mordre vs mare

A pond, sounds similar but shorter.

Idioms & Expressions

"S'en mordre les doigts"

— To experience intense regret for a past action.

J'ai raté l'occasion et je m'en mords les doigts.

neutral

"Mordre la poussière"

— To be defeated, to fail, or to die.

Le champion a fini par mordre la poussière.

literary

"Mordre à pleines dents"

— To enjoy something (like life) with great enthusiasm.

Il faut mordre la vie à pleines dents.

informal

"Mordre à l'hameçon"

— To fall for a trick or a trap.

Il a mordu à l'hameçon de ce faux site web.

neutral

"Un froid à mordre"

— Extremely cold weather that feels like it's biting the skin.

Couvre-toi bien, il fait un froid à mordre.

informal

"Mordre au vif"

— To hurt someone's feelings deeply or touch a sensitive point.

Sa critique l'a mordu au vif.

neutral

"Mordre sur le temps"

— To take up time that was meant for something else.

Le travail mord souvent sur ma vie de famille.

neutral

"Ne pas mordre"

— To refuse to take the bait or show interest.

J'ai proposé une réduction, mais il n'a pas mordu.

neutral

"Mordre la ligne"

— To commit a foul in sports by stepping over a boundary.

C'est un essai nul car il a mordu la ligne.

neutral

"Mordre à la grappe"

— To be completely deceived by a story.

Elle a mordu à la grappe quand il a raconté son mensonge.

informal

Easily Confused

mordre vs piquer

English uses 'bite' for insects.

Piquer is for stings/pricks, mordre is for teeth.

Le moustique pique, le chien mord.

mordre vs ronger

Both involve teeth.

Ronger is continuous gnawing, mordre is a single bite.

Le castor ronge l'arbre.

mordre vs mâcher

Both involve the mouth.

Mâcher is the act of chewing repeatedly.

Il mâche du chewing-gum.

mordre vs grignoter

Both involve eating.

Grignoter is small, frequent bites (nibbling).

Elle grignote devant la télé.

mordre vs croquer

Both involve biting.

Croquer implies a crunching sound.

Croquer un biscuit.

Sentence Patterns

Le [animal] mord.

Le chien mord.

Je mords dans [food].

Je mords dans une orange.

Je me suis mordu [body part].

Je me suis mordu le doigt.

Il a mordu à [trap/bait].

Il a mordu à l'arnaque.

Tu vas t'en mordre les doigts.

Si tu pars, tu vas t'en mordre les doigts.

[Something] mord sur [space/time].

La cour mord sur la rue.

Un ton [adjective] et mordant.

Un ton vif et mordant.

Mordre la poussière.

L'empire a mordu la poussière.

Word Family

Nouns

morsure (a bite)

mordant (sharpness/etching fluid)

mors (a bit for a horse)

Verbs

remordre (to bite again)

démordre (to let go/change mind)

Adjectives

mordant (biting/sharp)

mordu (bitten/fanatic)

dent

mâchoire

dentition

canine

incisive

How to Use It

frequency

High in daily life and idioms.

Common Mistakes

Le moustique m'a mordu. → Le moustique m'a piqué.
Insects 'piquent' (sting/prick) in French, they don't 'mordent'.
Je mords ma langue. → Je me mords la langue.
Reflexive actions on the body use 'se' and the definite article.
Je morde la pomme. → Je mords la pomme.
The present tense ends in -ds, not -de for third-group verbs.
J'ai mordu l'hameçon. → J'ai mordu à l'hameçon.
The idiom requires the preposition 'à'.
Il a mordu sur ma vie. → Cela mord sur ma vie.
Ensure the subject is the thing doing the encroaching.

Tips

The 'd' stays

In the singular present tense, always keep the 'd': Je mords, Tu mords, Il mord. Don't drop it!

Biting into food

Always use 'dans' when biting into a piece of food. 'Je mords dans la pomme' is more natural than 'Je mords la pomme'.

Taking the bait

Use 'mordre à l'hameçon' for literal fishing and for being tricked by a scam.

Insects don't bite

Never use 'mordre' for mosquitoes or bees. Use 'piquer' instead.

Finger biting

Memorize 's'en mordre les doigts'. It is one of the most common ways to say 'I really regret that' in French.

Sports foul

If you are watching the Olympics in French, 'mordre' is the word for a foul line violation.

Sharp wit

Use 'mordant' to describe a person with a sharp, sarcastic sense of humor.

Reflexive body parts

When you bite yourself, use 'se mordre' + 'le/la/les'. 'Je me mords la lèvre'.

The final 'dre'

The final 'dre' is very short. It's almost just a puff of air after the 'd' and 'r'.

Encroachment

Use 'mordre sur' when one thing is taking up space belonging to another, like a building on a sidewalk.

Memorize It

Mnemonic

Imagine a dog named 'Mordred' who likes to 'mordre' (bite) everything in the 'mord' (moat).

Visual Association

Picture a bright red apple with a large bite mark out of it. The 'mor' in mordre sounds like 'more'—you want 'more' bites of the apple.

Word Web

morsure dent chien pomme regret mordant ligne hameçon

Challenge

Try to use 'mordre' in three different ways today: one for an animal, one for food, and one for an idiom.

Word Origin

From the Latin 'mordere', which means 'to bite' or 'to devour'.

Original meaning: To seize with the teeth.

Indo-European (Italic > Romance).

Cultural Context

Be careful when using 'mordre' with people; it can imply physical assault or extreme aggression unless used reflexively (biting one's own lip).

English speakers often use 'bite' for insects, but in French, this is a major error. You must use 'piquer'.

The movie 'Le Mors aux dents' (1979). La Fontaine's fables often feature animals that 'mordent'. The idiom 'mordre la poussière' is the title of many French translations of Westerns.

Practice in Real Life

Real-World Contexts

At the park

Est-ce qu'il mord ?
Mon chien ne mord pas.
Attention, il va mordre !
Il a mordu la laisse.

At the dinner table

Mordre dans le pain.
Je me suis mordu la joue.
Ne mords pas tes couverts.
Il mord à pleines dents.

In a sports competition

Il a mordu la ligne.
Essai mordu.
Ne pas mordre le trait.
Disqualifié pour avoir mordu.

Discussing a scam

Il a mordu à l'hameçon.
Ne mords pas à ses mensonges.
Elle a mordu à l'appât.
Ils ont mordu à la grappe.

Expressing regret

Je m'en mords les doigts.
Tu t'en mordras les doigts.
Il s'en mordra les doigts.
S'en mordre les doigts amèrement.

Conversation Starters

"As-tu déjà été mordu par un animal ?"

"Est-ce que tu mords dans les pommes ou est-ce que tu les coupes ?"

"T'es-tu déjà mordu la langue en parlant trop vite ?"

"Connais-tu quelqu'un qui a un humour très mordant ?"

"As-tu déjà regretté quelque chose au point de t'en mordre les doigts ?"

Journal Prompts

Décris une fois où tu as mordu à l'hameçon d'une plaisanterie.

Pourquoi dit-on qu'il faut mordre la vie à pleines dents ?

Raconte une expérience sportive où quelqu'un a mordu la ligne.

Est-ce qu'un climat froid et mordant te dérange ?

Écris sur un regret dont tu te mords encore les doigts aujourd'hui.

Frequently Asked Questions

10 questions

No, you must use 'piquer'. 'Mordre' requires teeth, which mosquitoes don't have in the way humans/dogs do. Say 'Un moustique m'a piqué'.

The past participle is 'mordu'. For example: 'Il a mordu'.

You say 'se ronger les ongles'. Even though you use teeth, the continuous action makes 'ronger' the correct verb.

It is a regular -re verb of the third group. It follows the same pattern as 'vendre' or 'perdre'.

It literally means 'to bite one's fingers about it'. It's used to express deep regret.

Yes, as an adjective 'mordant' (biting) or sometimes 'le vent mord le visage' in poetic contexts.

It is 'nous mordons'. You keep the 'd' and add 'ons'.

In sports, 'mordre la ligne' specifically means your foot touched the line when it shouldn't have.

No, but 'mordre à' can mean you are starting to understand or be interested in something (like a project 'taking' or 'biting').

Yes, 'un mordu' is a slang/informal term for a fan or an enthusiast. 'Un mordu de foot' is a football fan.