입이 싸다.

This phrase means a person talks too much about secrets. '입' is mouth. '싸다' is cheap. It is like saying 'Your mouth is cheap.' Use it when a friend tells your secret to others. It is not a nice thing to say, so be careful!

The idiom '입이 싸다' describes someone who cannot keep a secret. In Korean, '싸다' usually means 'cheap' in price, but here it means the person's words are not careful. If you tell an '입이 싼 사람' (loose-lipped person) a secret, everyone will know it tomorrow. The opposite is '입이 무겁다' (the mouth is heavy).

This idiomatic expression is used to criticize someone's lack of discretion. When we say someone's mouth is 'cheap' (싸다), we imply that they distribute information too freely without considering its value or the trust involved. It is frequently used among friends or coworkers to warn others about a gossip. While '입이 가볍다' (light mouth) is a common synonym, '입이 싸다' carries a slightly stronger negative nuance, suggesting the person's character is somewhat shallow.

In Korean interpersonal dynamics, '입이 싸다' serves as a cautionary label for individuals who fail to uphold the social contract of confidentiality. The metaphor of 'cheapness' suggests that the individual treats sensitive information as a low-value commodity to be traded for social attention. This phrase is particularly relevant in the context of 'Gwan-gye' (relationships), where the ability to guard secrets is a primary measure of one's reliability and social maturity. Learners should distinguish this from '입이 짧다' and use '입이 무겁다' when they want to praise someone's trustworthiness.

The idiom '입이 싸다' encapsulates a profound socio-linguistic critique of verbal indiscretion. By utilizing the adjective '싸다' (to be cheap/inexpensive), the Korean language equates the act of gossiping with the devaluation of one's own speech and the breach of communal trust. This expression functions within a broader framework of 'Chemyeon' (social face), where the inability to contain information is viewed as a lack of self-control and dignity. Advanced learners should note the subtle register shifts between '입이 싸다' and '입이 가볍다,' the former being more colloquial and pointedly derogatory, often used in venting or informal warnings.

From a cognitive linguistic perspective, '입이 싸다' employs an economic metaphor to map the domain of 'value' onto 'verbal communication.' The 'cheapness' of the mouth signifies a low threshold for information discharge, reflecting a perceived deficit in the speaker's 'social capital' and 'ethical weight.' This idiom is a quintessential example of how Korean cultural values—specifically those pertaining to the sanctity of shared secrets and the maintenance of group cohesion—are encoded into everyday language. Mastery involves not only understanding the literal-to-figurative transition but also navigating the delicate pragmatics of when such a blunt characterization is socially permissible versus when it might be seen as an overstep by the speaker themselves.