Green’s Dictionary of Slang

1. a person or thing of outstanding quality, attractiveness or excellence.

1892		Albert Chevalier ‘Our Little Nipper’ 🎵 Do me proud well ’e’s a knock out, Takes after me and ain’t a bit too tall.
1895		Riverina Recorder (Moulamein, NSW) 3 July 2/7: [T]he Canally boys intend their social to be a regular ‘knock out’.
1899		Fieldhouse & LeBrunn [perf. Gus Elen] ‘The Coster’s Mansion’ 🎵 It’s a knock-aht, is this domicile o’ mine.
1905		H. Green Actors’ Boarding House (1906) 282: But, by George! The kid in the back row; that was a knockout. And he’d never spoken to her.
1905		H.G. Wells Kipps (1952) 200: That poem knocked me! I won’t say that Kipling hasn’t knocked me before and since, but that was a Fair Knock Out.
1914		R. Tressell Ragged Trousered Philanthropists (1955) 475: As for the plum pudding – it was a fair knock-out.
1914		C. Holme Lonely Plough (1931) 227: There was a hat he thought would look a regular knock-out on Francey.
1920		H.C. Witwer No Base Like Home 15: You small time knockouts are all alike — world beaters with the high school boys.
1926		Boys’ Realm 16 Jan. 265: Horace was full of admiration. ‘You’re a knock-out!’ he exclaimed.
1926		Judge (NY) 91 July-Dec. 31: Knock Out - Pretty girl.
1930		D. Hammett Maltese Falcon (1965) 295: You’ll want to see her anyway: she’s a knockout.
1941		K. Tennant Battlers 21: You’d be a knockout outside the pubs on a Saturday afternoon. [...] We’d coin money.
1948		C. Day Lewis Otterbury Incident 96: For the apparition at the door was a knock-out.
1953		S. Bellow Augie March (1996) 314: It [i.e. a jacket] was a knockout, with a dozen different kinds of pockets.
1956		J. Curtis Look Long Upon a Monkey 31: In his own opinion he was a knock-out for looks and, though delighted as a vain girl, he enjoyed repulsing with obscene brutality the perverts’ constant attentions.
1957		H. Nielsen ‘Decision’ in Best of Manhunt (2019) [ebook] ‘You’ll be a knockout in an evening gown’.
1960		Wodehouse Jeeves in the Offing 29: Nobody could have called him a knock-out in the way of looks.
1970		T. Southern Blue Movie (1974) 48: Having that kid didn’t affect her figure one bit — she’s still a knockout!
1978		P. Theroux Picture Palace 26: One was a knockout – a Spanish girl squatting with her skirt hiked up to her waist.
1984		‘Derek Raymond’ He Died with His Eyes Open 77: She was a real knockout at eighteen.
1997		C. Hiaasen Lucky You 298: Mary Andrea Finley Krome sparkled like a movie star. [...] Even the managing editor admitted she was a knockout.
1999		Indep. Rev. 5 Nov. 11: For all that, The Sixth Sense isn’t quite the knock-out we’ve been promised.
2000		Guardian 31 Mar. 21: Di-Caprio is a total knockout.
2004		E. Weiner Drop Dead, My Lovely (2005) 157: A hundred drop-dead knockouts working the counters.
2012		L. Berney Whiplash River [ebook] She was still a knockout.
2023		(con. 1962) J. Ellroy Enchanters 11: She’s a schoolmarm knockout in a summer shoft dress.

2. a pleasant, gratifying surprise.

1901		‘Hugh McHugh’ Down the Line 43: ‘Barnes [...] do you smoke?’ It was a knock-out. In the annals of the road no one could look back to the proud day when Sledgeheimer had coughed.
1906		E. Dyson Fact’ry ’Ands 183: These reflections flowed in upon him, despite the fact that it was ‘a fair knock out’.
1924		H.L. Wilson Professor How Could You! 147: I handed your little playmate a knockout (a surprise).
1939		J. Weidman What’s In It For Me? 10: If this was a surprise, the rest of it was going to be a knock-out.
1945		‘Henry Green’ Loving (1978) 79: Well then isn’t this a knock out?
1959		B. Hecht Sensualists (1961) 58: You’re a knockout [...] When I heard you wanted to see me, I got ready for a real rough-and-tumble.

3. a complete success.

1914		Ade ‘The New Fable of the Uplifter’ in Ade’s Fables 111: If they would [...] leave the Artists fatten up their Scenes, probably the Bloomer could be converted into a Knock-Out.
1926		Wood & Goddard Dict. Amer. Sl. 28: knock out, K.O. To win by knocking pugilistic opponent unconscious; a complete success in anything.

4. (US Und.) the ‘badger game’, where a man is blackmailed after being lured into a compromising situation with a prostitute.

1910

Committee of Fourteen Social Evil in N.Y. City 62: They take their places in the ranks, first as the protector of one woman, [...] and as accomplices in ‘knock-out’ cases, robberies, and other forms of vice.

5. a ‘knockout’ drug or potion; also attrib.

1896		F. Hutcheson Barkeep Stories 46: ‘Cripple Creek guys’ll do to you if dey ketch you trowin’ de knockout into anybody’.
1896		F. Hutcheson Barkeep Stories 44: ‘[D]o you know anyt’ing ’bout dat knock-out graft? [...] givin’ a guy de dope to put him out so’s y’ kin cop wot coin he has’.
1902		Wash. Times (DC) 14 Sept. 10/4: Knockout — A drug.
1909		H. Green Mr. Jackson 53: Bill slipped the knockout into his booze.
1930		‘Leslie Charteris’ Enter the Saint 212: She thought I was so crazy about her that I was as soundly doped that way as I could have been doped by a gallon of ‘knock-out.’.
a.1948		(con. early 1930s) C. McKay Harlem Glory (1990) 87: That hooch is a knock-out [...] I believe it’s responsible for most of the crazy-acting people in Harlem.

6. see knock n.¹ (2b)