We’ve used the term “rat” to refer to an informer since approximately 1910. But Eric Partridge’s Dictionary of the Underworld, published first in 1949 with a second edition in 1961, shows that in the Cant language of the underworld—which first appeared in Britain in the 16th century and the United States in the 18th—criminals have many more names for snitches. Here are some of them.
1. Abaddon: This term dates to circa 1810-80 and means "a thief who informs on his fellow rogues." It comes from the Hebrew abaddon, a destroyer.
2. Bark: Similar to "to squeak" and "to squeal," bark, as defined by the 1889 glossary Police!, meant "to inform (to the police)." It was obsolete by 1930.
3. Beefer: In the 1899 glossary Tramping with Tramps, Josiah Flynt writes that a beefer is "One who squeals on, or gives away, a tramp or criminal." By the 1930s, the word—American in origin—had moved from tramps to become slang for police and journalists, according to Partridge.
4. Bleat: Lambs aren't the only ones who do this. When informants bleat, they give information to the police. Partridge cites November 8, 1836's The Individual: "Ven I'm corned, I can gammon a gentry cove, Come the fawney-rig, the figging-lay, and never vish to bleat." The term was obsolete in Britain by 1890, but as of 1920 was a current slang term in the U.S.
5. Blobber: According to Henry Leverage's "Dictionary of the Underworld" from Flynn's magazine, this is an American term for an informer from early 1925.
6. Blue: A verb meaning "to blew it; to inform (to the police)," according to the H. Brandon's 1839 book Poverty, Mendicity and Crime, and J.C. Hotten's The Slang Dictionary from 1859. It was common slang by 1890, as noted in Farmer & Henley's Slang and its Analogues.
7. Cabbage Hat: A mostly Pacific Coast term for an informer, circa 1910; a rhyming on rat, according to D.W. Mauer and Sidney J. Baker's "'Australian' Rhyming Argot in the American Underworld," which appeared in American Speech in October 1944.
8. Crysler: A punny reference (of American origin) to Chrysler cars meaning "a squealer; a traitor; a coward," according to Leverage's "Dictionary of the Underworld."
9. Cocked Hat: Another Pacific Coast rhyme on rat, circa 1910, that means "informer to the police."
10. Come Copper: A 1905 term for someone who gave information to the police.
11. Come it / Come it as strong as a horse: Come it (or, verbally, coming it) dates back to 1812, and means to be an informer. "Come it strong" meant to do a thing vigorously, and according to Egan's Grouse in 1823, "They say of a thief, who has turned evidence against his accomplices, that he is coming all he knows, or that he comes it as strong as a horse."
12. Conk: As a noun, conk dates back to the early 1800s and means "a thief who impeaches his accomplices; a spy; informer, or tell tale." As a verb, it means to inform to the police, and was often verbally called "conking it." Conk was obsolete by 1900.
13. Dropper Man: An Australian term, circa 1910, for a habitual informer to the police. "A man that drops information; also, he causes men to 'drop' or 'fall' (be arrested)," notes Sidney J. Baker in 1945's The Australian Language.
14. Finger Louse: This American term, dating back to the 1930s, is an elaboration of finger, meaning to take the fingerprints of a person.
15. Fizgig / Fizzgig: This slang term for an informer, circa 1910, may have derived from fizgig, Australian for "fishing spear." "Often shorted to fiz(z)," Partridge writes. "By contemptuous euphemism; not unrelated to thingamyjig."
16. Grass: This word—short for grasshopper (circa 1920), rhyming on copper—dates back to the 1930s. "Come grass" is also used to describe someone who informs to the police.
17. Knock-Down: Giving information to police, circa 1910.
18. Lemon: A 1934 American term meaning "one who turns State's evidence" because he has "turn[ed] sour on his confederates."
19. Narking Dues: Partridge says this British phrase is "used when someone has been, or is, laying information with the police." It appeared in 1896's A Child of the Jago:
Presently, he said: "I bin put away this time . . ." — "Wot?" answered Bill, "narkin' dues is it?" — Josh nodded. — "'Oo done it then? 'Oo narked?"
The term was obsolete by 1940, but the word "nark" lives on.
20. Nose / To Nose / Turn Nose: Nose is a 1789 word for a snitch; to nose or turn nose, both circa 1809, meant to give evidence or inform.
21. On the Erie: A 1933 term, American in origin, for someone who makes a living by informing to the police, i.e., "That mug has always been on the Erie." (This term can also mean "shut up! Someone is listening.")
22. Pigeon: An American verb, dating back to 1859, meaning to inform to the police.
23. Puff: A British term for a King's informer, dating back to 1735; obsolete by 1890.
24. Quatch: An American term, circa 1925, meaning "to betray secrets." Similar to quack, a verb meaning "to inform to the police," and quag, "unsafe, not reliable; not to be trusted."
25. Scream: A noun, circa 1915, for "the giving of information to police, especially by one criminal against another." Partridge notes that by 1920, it began to mean the same as to squeal. From 1915's The Melody of Death:
"I don't want to hear any more about your conscience," said the [police] officer wearily. "Do you scream or don't you?"
By 1925, the term had hopped across the pond from England to the United States.
26. Snake in the Grass: An American term for an informer who conceals his informing, circa 1925.
27. Snickle: A confusion of snitch and snilch, this American term meaning "to inform to the police" dates back to 1859; it was obsolete by 1920.
28. Telegram: Australian term, circa 1899, for a spy or informer.
29. Turn Chirp: A British term from 1846 for turning the King's evidence. Comes from G.W.M. Reynolds' "The Thieves' Alphabet," in The Mysteries of London: "N was for a Nose that turned chirp on his pal." Partridge wonders, "Does it exist elsewhere?"
30. Viper: An American term, circa 1925. "Contemptuous," Partridge notes, "'a snake in the grass.'"
31. Weak Sister: This term dates back to 1924, and doesn't just mean an informer, but "an untrusted person, or a weakling, in a gang."