pigeon

A person who is easily exploited, deceived, or taken advantage of, especially due to being in a position of vulnerability. Likened to the clay pigeons (small clay discs) used as targets in trapshooting. Primarily heard in US, South Africa. He was used as a clay pigeon by the mafia, who laundered money through his accounts.

To be one's area of expertise or responsibility. Primarily heard in UK, Australia. I can't approve expense reports, but Betty can—that's her pigeon.

An informant, especially a criminal working as a spy for law enforcement officers. Although the criminal agreed to help the police in order to avoid prison time, he was afraid the other gang members would kill him if they discovered he was a stool pigeon.

to do or say something that causes trouble and makes a lot of people angry or worried Tell them all they've got to work on Saturday. That should set the cat among the pigeons.

if something is someone's pigeon, they are responsible for it Finance isn't my pigeon. Ask Brian about that.

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.

A person easily duped or taken advantage of, as in You're a clay pigeon for all of those telephone fund-raisers. The term alludes to the clay pigeon of trapshooting, which replaced the use of live birds in this sport in the 1860s. Its transfer to figurative use in the first half of the 1900s probably is explained by the much older slang use of pigeon for "dupe." Also see fall guy.

A decoy or informer, especially a police spy. For example, Watch out for Doug; I'm sure he's a stool pigeon for the supervisor. This term alludes to a bird tied to a stool or similar perch in order to attract other birds, which will then be shot. However, one writer believes that stool is a variant for stale or stall, both nouns used for a decoy bird before 1500 or so. [c. 1820]