informer

Compared meaning: someone who tells authorities about others' wrongdoing (noun).

比较义项：告密者、向当局告发他人的人（名词）。

• rat

  Informal, strongly disapproving slang for someone who betrays friends, colleagues or their own group by informing on them, typically to police or authorities.

  非正式且带强烈贬义色彩的俚语，指背叛朋友、同事或自己所属群体、向警方或当局告发他们的人。

  Some inmates consider Jake a rat because he told the guards about the escape plan.

  一些囚犯认为杰克是个叛徒，因为他把越狱计划告诉了狱警。

• informer 本词

  Neutral, more formal term for someone, often paid, who supplies information about illegal activity to the police; does not necessarily imply betraying one's own friends or group.

  较为中性、正式的说法，指向警方提供非法活动信息的人，此人常常收取报酬，并不一定意味着背叛自己的朋友或群体。

  The detective paid an informer for details about the gang's smuggling operation.

  那名警探花钱收买了一名告密者，以获取该团伙走私活动的细节。

Rat and informer both mean someone who reports wrongdoing to authorities. Rat is informal slang, strongly negative, stressing betrayal of one's own friends or group. Informer is neutral and formal, common in police contexts, without necessarily betraying acquaintances. Not compared: rat meaning the animal.

rat 和 informer 都指把他人的不法行为告诉当局的人，但语气和正式程度不同：rat 是非正式俚语，带强烈贬义，强调背叛自己的朋友、同伙或所属群体；informer 更中性、正式，常见于警方语境，不一定涉及背叛熟人，也可能是收费提供消息的人。这里不比较 rat 的“老鼠”这一动物义项。