Pigeons aren’t particularly talkative birds. They prefer to spend their time on window sills and park statues rather than ottomans, all of which leads us to believe that the expression stool pigeon wasn’t originally meant to be taken literally.
Indeed, several sources (including the Online Etymology Dictionary) indicate that the term most likely evolved from the Old French word estale, which dates back to the 1400s and was used to describe a decoy bird (often a pigeon) used to lure birds of prey into a net. When it entered the English language, the initial e was dropped from the word and stale was used to refer to a person or thing used as a lure to entrap a person. (William Shakespeare was referring to burglar bait when he wrote “The trumpery in my house, go bring it hither for stale to catch these thieves” in The Tempest.)
The phrase stool pigeon first appeared sometime during the early 1800s, with Noah Webster using it to describe a pigeon hunting tactic where a pigeon was tied to a moving stool to make the bird flutter and attract a large flock of pigeons for easy catching. But the animal uses are relatively rare compared to the frequency with which the phrase is used to describe people who infiltrated a criminal enterprise and then reported back to law enforcement personnel with their findings just to curry favor with the local cops. The first uses of stool pigeon to describe police informers occurred in the 1840s, according to the Oxford English Dictionary.
Many etymologists think that the association between the phrase and an actual physical stool pigeon is a false etymology, not least of all because references to the hunting method are extremely rare, while references to it as a person are common.
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A version of this story ran in 2016; it has been updated for 2023.