a. That knocks out; characterized by knocking out; as, a knock-out blow; a knock-out key for knocking out a drill from a collet. [ Webster 1913 Suppl. ]

n. Act of knocking out, or state of being knocked out; the act of rendering a person unconscious by a blow. [ wns=1 ] [ Webster 1913 Suppl. + WordNet 1.5 ]

2. a blow which causes a person to become unconscious.
Syn. -- knockout blow, knockout punch. [ WordNet 1.5 ]

3. (Boxing) the winning of a boxing contest by rendering the opponent unable to stand for a specified period, usually a count of ten; -- in contrast to a win by a decision; as, Muhammed Ali won by a knockout in the first round. [ WordNet 1.5 ]

4. a strikingly beautiful woman. [ Informal ] [ PJC ]

n. pl. Drops of any drug, used to a person to fall asleep or become unconscious or stupefied for the purpose of robbery, etc.; they are usually mixed into a drink so that the person consuming it does so unknowingly. One compound used for this purpose is chloral hydrate. [ Slang, U. S. ] [ Webster 1913 Suppl. + PJC ]