a stool pigeon

a person, especially a criminal, who secretly gives information to the police in order to help them catch other criminals Once they discovered he was a stool pigeon, it was only a matter of time before they had him killed.

Common Names:

Name	Pronounced	Usage
Law	[lɔ:]
Augusta	ow-GUWS-tah (German, Polish), ow-GOOS-tah (Italian), ə-GUS-tə (English)	German, Italian, Portuguese, Polish, Dutch, English, Ancient Roman
Russ	[rʌs]
Alyson	AL-i-sən	English
Iliana	-	Greek, Bulgarian
Aurelius	[ɔ:'ri:jəs]