Green’s Dictionary of Slang

k.o. n.

also kayo
(orig. US)

1. a knockout; also fig. use.

[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 53: Sleepy Mickey Finnegan who took a fine lacing for a round then put the k.o. on his man.
[US]Salt Lake Trib. 23 Feb. 27/1: Little ‘Kayo’ Brown finished flat on his back.
[NZ]N.Z. Truth 9 Jan. 6/1: [headline] Australian Scores K.O. in Round One.
[US]T.A. Dorgan in Zwilling TAD Lex. (1993) 51: Champion Has Two Sets To Kayo.
[US]W.R. Burnett Iron Man 26: Speed won by a K.O.
[US]W. Winchell ‘On Broadway’ 15 Nov. [synd. col.] When he wanted to be sure of a quick kayo, he’s put one [i.e. roll of nickels] in each fist.
[US]B. Schulberg Harder They Fall (1971) 8: Frank [...] had him on the verge of a kayo in the early rounds.
[US]‘Ed Lacy’ Lead With Your Left (1958) 8: Ten amateur fights with nine kayos. Nine kayos, Mrs. Wintino.
[UK]A. Sinclair Breaking of Bumbo (1961) 93: All we are is a lousy punch-drunk ex-champ, between a couple of real big men, jockeying around for the K.O.
[US]F. Salas Tattoo the Wicked Cross (1981) 28: A professional fighter with a string of kayos to his credit.
[Aus]S. Gore Holy Smoke 14: Down he goes with a lump on his scone like a rockmelon. A straight K.O.
[UK]G. Young Slow Boats to China (1983) 43: As a boxer will study an opponent on film to decide whether to take it slow and tricky or go for a kayo in the first round.
[US]W.T. Vollmann You Bright and Risen Angels (1988) 325: This was K.O. on the O.K.
[US]T. Jones Pugilist at Rest 66: I lost on a K.O.
[US]F.X. Toole Rope Burns 16: Two wins by kayo.
[SA]IOL News SA 20 Oct. [Internet] Chiefs suffer another early KO [...] a party atmosphere matched by a five-goal Telkom knockout thriller.

2. in fig. use, death or termination.

[US] letter in K.F. Cowing Dear Folks at Home (1919) 215: Everyone of their American boys are putting the K.O. on the Big, Brave, and Best German soldiers.
[UK]V. Davis Gentlemen of the Broad Arrows 199: We all thought you had taken the K.O.
[US]E. O’Neill Iceman Cometh Act III: Some party last night, huh? Jees, what a funeral! It was jinxed from de start, but his tellin’ about his wife croakin’ put de K.O. on it.

3. attrib. use of sense 2.

[UK] (ref. to 1920s) L. Duncan Over the Wall 71: This was almost a kayo punch good for a ten count.
[Aus]L. Glassop Lucky Palmer 125: A middleweight with a K.O. punch in either mitt.
[US]N. Algren ‘Watch Out for Daddy’ in Entrapment (2009) 136: [of knock-out drops] It’s time to go the kayo route, Baby.
[UK]N. Barlay Hooky Gear 8: I done ju-jitsu an busted Duanes KO hand one time.

In compounds