Green’s Dictionary of Slang

knockout n.

[knock out v. (2a)]

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

[UK]Albert Chevalier ‘Our Little Nipper’ [lyrics] Do me proud well ’e’s a knock out, Takes after me and ain’t a bit too tall.
[UK]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.
[UK]R. Tressell Ragged Trousered Philanthropists (1955) 475: As for the plum pudding – it was a fair knock-out.
[UK]C. Holme Lonely Plough (1931) 227: There was a hat he thought would look a regular knock-out on Francey.
[US]W.C. Witwer No Base Like Home 15: You small time knockouts are all alike — world beaters with the high school boys.
[UK]Boys’ Realm 16 Jan. 265: Horace was full of admiration. ‘You’re a knock-out!’ he exclaimed.
[US]Judge (NY) 91 July-Dec. 31: Knock Out - Pretty girl.
[US]D. Hammett Maltese Falcon (1965) 295: You’ll want to see her anyway: she’s a knockout.
[Aus]K. Tennant Battlers 21: You’d be a knockout outside the pubs on a Saturday afternoon. [...] We’d coin money.
[US]S. Bellow Augie March (1996) 314: It [i.e. a jacket] was a knockout, with a dozen different kinds of pockets.
[UK]Wodehouse Jeeves in the Offing 29: Nobody could have called him a knock-out in the way of looks.
[US]T. Southern Blue Movie (1974) 48: Having that kid didn’t affect her figure one bit — she’s still a knockout!
[UK]‘Derek Raymond’ He Died with His Eyes Open 77: She was a real knockout at eighteen.
[US]C. Hiaasen Lucky You 298: Mary Andrea Finley Krome sparkled like a movie star. [...] Even the managing editor admitted she was a knockout.
[US]E. Weiner Drop Dead, My Lovely (2005) 157: A hundred drop-dead knockouts working the counters.

2. a pleasant, gratifying surprise.

[US]‘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.
[Aus]E. Dyson Fact’ry ’Ands 183: These reflections flowed in upon him, despite the fact that it was ‘a fair knock out’.
[US]H.L. Wilson Professor How Could You! 147: I handed your little playmate a knockout (a surprise).
[US]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.
[UK]‘Henry Green’ Loving (1978) 79: Well then isn’t this a knock out?
[US]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.

[US]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.
[US]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.

[US]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.

[US]F. Hutcheson Barkeep Stories 46: ‘Cripple Creek guys’ll do to you if dey ketch you trowin’ de knockout into anybody’.
[US]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’.
[US]Wash. Times (DC) 14 Sept. 10/4: Knockout — A drug.
[US]H. Green Mr. Jackson 53: Bill slipped the knockout into his booze.
[UK]‘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.’.
[US](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)

In phrases

to a knockout

(US) to the greatest extent possible.

[US]C. Connors Bowery Life [ebook] Dancin? Sure. All de workin’ fellers could hev der steadies an’ twist ter a knockout.