stool pigeon
告密者，卧底警察或间谍用来从内部收集信息的人
口语·形容告密者或线人
英文释义
a person who provides information or acts as an informant, often for the police
例句
The police caught the thief because a stool pigeon tipped them off.
典故来源
源自捕鸟时用鸽子作诱饵的习俗，比喻向警方告密的人。