stool pigeon
告密者，臥底警察或間諜用來從內部收集信息的人
口語·形容告密者或線人
英文釋義
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.
典故來源
源自捕鳥時用鴿子作誘餌的習俗，比喻向警方告密的人。