The act of making one unconscious, or at least unable to come back on one's feet within a certain period of time; a TKO.
The boxer scored a knockout on his opponent.
2
The deactivation of anything.
Pull the plug on a node to see how the network handles a node knockout.1989 February 6, Network World, page 82:
3
Informal Something wildly popular, entertaining, or funny.
If you've ever had a sack race, you know it's a real knockout for kids and adults alike.
4
Informal A very attractive person, especially a beautiful woman.
“There’s a girl wants to see you. Her name’s Wonderly.” “A customer?” “I guess so. You’ll want to see her anyway: she’s a knockout.”1930, Dashiell Hammet, The Maltese Falcon, New York, N.Y.; London: Alfred A[braham] Knopf, →OCLC, page 3:
"You’re asking too many questions. Look. You’re a cute kid. I mean, you’re a hell of a chick. You’re a knockout. But don’t go thinking you’re too important at this stage."1992, Neal Stephenson, Snow Crash, New York: Bantam Books, →ISBN, page 183:
2 more examples
Phrases such as "she bowled me over," "she's striking," and "she's a knockout" suggest that the woman affects the man in ways he cannot mediate or control.1995, Rhonda K. Reinholtz, “Sexual Discourse and Sexual Intercourse”, in P. J. Kalbfleisch, M. J. Cody, editors, Gender, Power, and Communications in Human Relationships, Routledge, →ISBN, page 150:
She was the "bikini-babe", "Sarkozette" stunna who never was. Paris was baffled this week when some of the British media began drooling over an old beach photograph of a former newsreader, Christine Kelly, whom they announced as Sarkozy's latest cabinet appointment—or rather "knockout lovely" or "oh yes, minister!".2009 March 28, Angelique Chrisafis, “The mystery of the bikini-clad minister”, in The Guardian, →ISSN:
5
A partially punched opening meant for optional later removal.
They left a knockout in the panel for running extra wires someday.
6
Biology, Genetics, Medicine, Natural sciences, Sciences The deactivation of a particular gene.
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Biology, Genetics, Medicine, Natural sciences, Sciences A creature engineered with a particular gene deactivated.
8
Media, Printing, Publishing An event where a foreground color causes a background color not to print.
9
Hobbies, Lifestyle, Sports A tournament in which a team or player must beat the opponent in order to progress to the next round.
the knockout stages of the competition
In truth, Tottenham never really looked like taking all three points and this defeat means they face a battle to reach the knockout stages -with their next home game against PAOK Salonika on 30 November likely to prove decisive.2011 November 3, Chris Bevan, “Rubin Kazan 1 – 0 Tottenham”, in BBC Sport:
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A simple game for two or more players, derived from basketball.
If the same model has beautiful hair, white teeth, glowing skin, a fit body, good hands and legs, a great wardrobe, and a knockout comp, her value on the "bookability meter" goes sky high.2010, Ro Martinez, Modeling at Any Age, page 81:
3
Biology, Genetics, Medicine, Natural sciences, Sciences Designating an organism in which a particular gene has been removed or deactivated.
The result is a so-called knockout mouse, reared with a single gene silenced, the better to reveal that gene's true purpose.1999, Matt Ridley, Genome, Harper Perennial, published 2004, page 255:
4
Causing elimination from a competition.
Rodolph Austin delivered the knockout blow from close range 20 minutes from time, after Aidan White had given Leeds a dream start after four minutes.2012, Ben Smith, Leeds United 2-1 Everton: