憎い

The core meaning of 膈い (nikui) is something that is hateful, detestable, or abominable. It describes a strong negative feeling towards a person, thing, or action.

Yes, it absolutely can. You can use it to describe someone you find hateful or detestable. For example: 彼はとても膈い人だ。 (He is a very hateful person.)

Yes, you can. It can describe a situation or thing that causes you great displeasure or feels abominable. For instance: その行為は膈い。 (That behavior is detestable.)

Yes, 膈い is a pretty strong word. It expresses intense dislike or hatred. It's not like simply 'disliking' something; it carries a much heavier emotional weight.

嫌い (kirai) means 'dislike' or 'hate', but it's generally a milder form of 'hate' compared to 膈い. 膈い implies a deeper, more profound sense of detestation or abomination. Think of 嫌い as 'I don't like it' and 膈い as 'I find it abominable/hateful'.

膈い (nikui) is an i-adjective, so it conjugates like other i-adjectives.
Negative: 膈くない (nikukunai) - not hateful
Past: 膈かった (nikukatta) - was hateful
Past Negative: 膈くなかった (nikukunakatta) - was not hateful

A common expression is 膈いもの (nikui mono), which translates to 'something hateful' or 'detestable thing'.
Example: 世の中には膈いものが多い。 (There are many hateful things in the world.)

While 膈い is generally a strong, serious word, in some specific contexts, particularly in casual speech or fiction, you might hear it used playfully or ironically to mean something like 'annoyingly good' or 'too clever for its own good'. However, for learners, it's best to stick to its primary, strong meaning first.

To form the adverbial form, you change the final い to く. So, 膈く (nikuku) can be used to modify verbs or other adjectives.
Example: 彼は膈く思われている。 (He is hated.)

Think of it as expressing a feeling that makes you want to 'nuke' something or someone out of existence because it's so detestable. (Disclaimer: This is just a mnemonic, not a reflection of the actual etymology!) Or, associate it with a strong, visceral reaction of disgust and hatred.