WordNet (r) 3.0 (2006):

kayo
    n 1: a blow that renders the opponent unconscious [syn:
         knockout, KO, kayo]
    v 1: knock unconscious or senseless; "the boxing champion
         knocked out his opponent in a few seconds" [syn: knock
         cold, knock out, kayo]

Moby Thesaurus II by Grady Ward, 1.0:

127 Moby Thesaurus words for "kayo":
   Cadmean victory, KO, Pyrrhic victory, anesthetize, ascendancy,
   bedaze, benumb, besot, blackout, blunt, call off, cancel,
   catalepsy, catatonia, catatony, championship, chloroform, clincher,
   coldcock, coma, complete, conquest, cook, crusher, deaden,
   death stroke, deathblow, defeat, delete, desensitize, dish,
   dispose of, do for, do in, dope, drop the curtain, drug, dull,
   easy victory, end off, end-all, ender, etherize, expunge,
   extinguish, faint, final stroke, finalize, finish, finisher,
   finishing stroke, fix, fold up, freeze, get it over, get over with,
   get through with, give the quietus, grand slam, grayout,
   kayo punch, kibosh, kill, knock out, knock senseless, knock stiff,
   knock unconscious, knockout, knockout blow, landslide,
   landslide victory, last dab, lay out, lipothymia, lipothymy,
   mastery, moral victory, narcotize, nirvana, nirvana principle,
   nothingness, numb, oblivion, obliviousness, obtund, palsy,
   paralyze, perfect, picnic, polish off, pushover, put paid to,
   put to sleep, quietus, runaway victory, scrag, scuttle,
   semiconsciousness, senselessness, settle, settler, shoot down,
   sink, sleep, sockdolager, stopper, stun, stupefy, stupor, subdual,
   subduing, success, swoon, syncope, torpedo, total victory, triumph,
   unconsciousness, undo, victory, walkaway, walkover, win, winning,
   winning streak, wipe out, zap