The Collaborative International Dictionary of English v.0.48:

KO \KO\ v. t. [imp. & p. p. KO'd; p. pr. & vb. n. KO'ing.]
   To knock out; to deliver a blow that renders (the opponent)
   unconscious; -- used especially in boxing. [acronym]

   Syn: knockout.
        [WordNet 1.5]