Green’s Dictionary of Slang

1. (also cap, capper-in) a confederate in a gambling game who poses as another gambler but actually works to swindle the genuine participants; similarly used in confidence tricks; also used of confidence tricksters (e.g. cite 1845) [such a confederate is always able to cap everyone else’s bet].

1753		J. Poulter Discoveries (1774) 31: There are generally four Persons concerned; that is, the Sailor, called a Legg Cull, to pinch the Nobb; the next is the Capper, who always keeps with the Sailor; and two Pickers up, or Money Droppers, to bring in Flats.
1762		O. Goldsmith Life of Richard Nash in Coll. Works (1966) III 347: There are generally four persons concerned in this fraud, one to personate a Sailor, called a Legg Cull, another called the Capper, who always keeps with the Sailor.
1777		J. Fielding Thieving Detected 30: When the Cap hath finished his story of him, the Kid comes in with a pack of cards [...] When the Kid has lost about ten or twelve guineas, he refuses to play any more with the Cap, he being so lucky – But I’ll play, says he, with either of these gentlemen. – Well are you agreeable says the Picker-up to the Flat.
1786		Whole Art of Thieving 8: The Art of Old Nobb, called Pricking in the Girdle. There are generally four persons concerned, that is, the sailor, called a Legg Cull, to pinch the Nobb; the next is the Capper, who always keeps with the sailor: and two pickers up, or Money Droppers, to bring in Flats.
1842		Whip & Satirist of NY & Brooklyn (NY) 16 July n.p.: There was the ‘thimble rigger’ [...] while his ever busy ‘capper in’ was here, there, and every where, on the look out.
1845		Nat. Police Gaz. (NY) 13 Dec. 133/3: On going down Broadway [...] he was accosted by a watch stuffer who, with the assistance of his pal or capper, endeavoured to stuff him with a mock watch.
1849		N.Y. Daily Globe 13 Mar. 2/5–6: What are you afraid of? – none of the New York Cappers are about. I know ’em all.
1853		Alta Calif. (S.F.) 25 Apr. 1/7: Each shop has a glib-mouthed auctioneer and at least two cappers, puffers, or decoy-ducks [DA].
1859		Matsell Vocabulum 17: capper. One who supports another’s assertion, to assist in cheating, ‘The burner bammed the file with sham books, and his pal capped in for him’ — The sharp cheated the countryman with false cards, and his confederate assisted (capped) in the fraud.
1867		Nat. Police Gaz. (NY) 7 Dec. 2/4: There will be so many ‘sheenies,’ ‘hoisters,’ ‘fences’ and ‘cappers’ on hand.
1873		J.H. Beadle Undeveloped West 92: The long hall is soon crowded with a motley throng of three or four hundred miners, ranchmen, clerks, ‘bullwhackers,’ gamblers and ‘cappers’.
1887		G. Devol Forty Years a Gambler 31: About this time the ‘capper’ came up, and said he was positive he could guess the card.
1896		J.F. Lillard Poker Stories 53: These cappers wouldn’t win any money.
1908		‘O. Henry’ ‘The Ethics of Pig’ in Gentle Grafter (1915) 228: Rufe was to be the capper. I gave him a roll of phony currency to bet with and kept a bunch of it in a special pocket to pay his winnings out of.
1915		Van Loan ‘The Spotted Sheep’ Taking the Count 118: Logan’s the main finger of the bunch – the boss. The others are cappers and steerers.
1926		J. Black You Can’t Win (2000) 151: His ‘cappers,’ ‘boosters,’ and ‘shills’ fought with the yokels for a chance to get something for nothing and always beat them to the pieces of soap containing the money.
1935		C.E. Mulford ‘Don’t Frame a Red Head’ in Western Fiction Monthly Aug. 🌐 He glanced around swiftly, trying to locate the cappers.
1949		R. Service ‘Montreal Maree’ in Songs of a Sun Lover (1955) 72: A satellite of Soapy Smith, a capper and a shill, / A slimy tribute-taker from the Ladies on the Loose.
1952		C. Hamilton Men of the Und. 320: Capper, An assistant to a confidence man or gambler.
2012		W. Keyser ‘Carny Lingo’ in http://goodmagic.com 🌐 Shill — Also ‘outside man,’ ‘stick,’ ‘capper,’ ‘front-worker’ or ‘timber.’ Employee who poses as a customer, playing a game (and being secretly allowed to win) or buying a ticket in order to motivate other customers to do likewis.

2. (US) an employee of a casino, brothel, strip-club etc, who points a potential client towards the variety of self-indulgence they seek [ext. use of sense 1].

1871		Galaxy (N.Y.) July 67: These are the canaille of gamblers, who [...] manage to supply the necessities of life in a cheap way, from chance success in small bets and by a few dollars picked up by guiding more profitable customers to the houses where they are known. Strictly speaking, more ‘cappers’ than gamblers, they are [...] at the bottom of the profession.
1901		C.R. Wooldridge Hands Up! 104: ‘Cappers’ are sent out to bring in the rural visitors. They are told of the ‘big sights’ to be seen in this wonderful place; shown pictures of women in suggestive attitudes and hear stories of a reproduction of a harem and this more easily leads out-of-town sightseers astray than anything else.
1903		Times Union (Brooklyn, NY) 18 Sept. 1/2: Passengers on the elevated trains [...] have been greatly annoyed by a number of men working a sweat board or shell game [...] They have with them a number of ‘cappers’ who have no difficulty in interesting the unwary.
1915		S. Ford Shorty McCabe on the Job 18: An ex-pool organizer, who makes a livin’ as capper for a hotel branch of a shady stock-brokin’ firm.
1919		C.S. Montanye ‘White as Snow’ Detective Story 18 Feb. 🌐 He returned to the city to turn capper for a gambling-house in the upper Forties.
1919		H.C. Witwer Smile A Minute 34: I [...] started to go out when the Plattsburg guy which acted like he was a capper for the show or somethin’ says to wait for the next act.
1929		M. Bodenheim Sixty Seconds 234: When the cappers on the floor — the men who tear the tickets — get a crush on a girl and she won’t tumble, they swear to the boss that she’s holding out on the tickets.
1938		H. Asbury Sucker’s Progress 415: A jostling mass of cappers, steerers, ropers-in and pickers-up, fighting over the suckers and literally dragging their prey into the gambling houses.
1940		H. Asbury Gangs of Chicago (2002) 73: In 1860, when he was about twenty-seven years old, he became a roper and capper for a small faro bank.
1950		Goldin et al. DAUL 40/2: Capper. [...] 2. One who directs or lures customers to a gambling den, house of prostitution, or other illegal resort. ‘Sadie’s nautcheries (brothels) got the hack-drivers and coppers in town on the payroll as cappers.’.
1960, 1975		Wentworth & Flexner DAS.
1993		I.L. Allen City in Sl. (1995) 73: Such places, also known as cab joints or steer joints, sometimes paid cab drivers, known as steerers or cappers, to bring them victims.

3. anything seen as terminal, ‘the last straw’.

1883		J. Keane On Blue Water 206: I’ve been in a few regular scorching hot packets, both Yanks and blue-nosers, but this puts the capper on the lot.
1906		S. Ford Shorty McCabe 195: As a capper he digs up that envelope, shows her there needn’t be any hitch in the program.
1929		K.S. Prichard Coonardoo 311: Bob had letters in his pocket for Hugh which would put the capper on all this misery and desolation.
1960		Jazz Rev. May 30: But dig, here’s the capper.
1970		Harper’s Mag. Nov. 55: It’s the capper to drugs. People were at the point where they were taking anything. It was insane. But they won’t go back now.
1979		G. Swarthout Skeletons 194: Played games with you and lied to you and tried to terrorize your ass and finally, for a capper [...] let you open up their godamned closet.
1981		J. Ellroy Brown’s Requiem 33: It was a capper to a frustrating morning.
1999		N. Cohn Yes We have No 287: And then, the capper [...] the motor was gone.
2012		C. Merrigan ‘Glinty-Eyed Robert’ in C. Rhatigan and N. Bird (eds) Pulp Ink 2 [ebook] I want to see the whores. To put the capper on this .

4. (US) a shop tout [ext. use of sense 1].

1901		C.R. Wooldridge Hands Up! 66: South side clothing ‘cappers’ rubbed their hands together in glee when the detectives passed them, offering them every inducement to come in and buy.
1924		O.O. McIntyre New York Day by Day 26 Nov. [synd. col.] A sleekly polished young blade who acts as a glorified capper for a jewelry firm. It is his job to steer patronage to his establishment.

5. an anecdote that steals the limelight from a previous anecdote, a punchline.

1943		Smith & Carnes American Guerrilla 47: And as a final ‘capper’ I asked my listeners to ponder another fact—that up to that moment guerrillas [...] had actually killed more Germans than the British and Americans.
1967		L. Bruce Essential Lenny Bruce 46: This would be a capper on Broadway.

6. (US black) one who triumphs in contests of verbal facility.

1970		R.D. Abrahams Positively Black It is not meant here that no one is considered the winner of such contests [i.e. ‘the dozens’], for certain men-of-words are regarded as inevitable cappers: .
1988		Too $hort ‘Cusswords’ 🎵 I’m a MC rapper [...] / A big bank roller and a cold, cold capper.