knockout

(nŏkˈoutˌ)

noun

1. a. The act of knocking out.
   b. The state of being knocked out.
   c. A blow that knocks out an opponent.
2. Sports
   a. A victory in boxing in which one's opponent is unable to rise from the canvas within a specified time after being knocked down or is judged too injured to continue.
   b. The act of winning a boxing match in this way: won the fight by a knockout.
3. Slang A strikingly attractive or impressive person or thing.

adjective also knock-out (nŏkˈoutˌ)

1. Capable of knocking out: a knockout punch.
2. Strikingly attractive or impressive.
3. Having a specific single gene removed from the genome by genetic manipulation: knockout mice used in an experiment.

Our Living Language An attractive or exciting person or thing can colloquially be called a knockout. First used in the early 20th century, this expression comes from a metaphorical use of the boxing term knock out. The sport of boxing has produced many terms, such as lightweight, heavyweight and slap happy that have entered our everyday language. Two political candidates will square off at the beginning of a debate, an expression with origins in the 18th- and 19th-century rules by which fighters began each round facing each other across a one-yard square in the center of the ring. One of our political candidates might anticipate a comment by the other and so beat her to the punch. If a candidate is clearly losing a debate, he may be said to be on the ropes, and he could even suffer a knockout blow, after which he might throw in the sponge or towel and quit his candidacy. Or, before any of that happens, perhaps time will run out on the other candidate, and he will be saved by the bell.