'knock out' definitions:

Definition of 'knock out'

(from WordNet)
verb
Eliminate; "knock out a target"
verb
Knock unconscious or senseless; "the boxing champion knocked out his opponent in a few seconds" [syn: knock cold, knock out, kayo]
verb
Destroy or break forcefully; "The windows were knocked out"
verb
Overwhelm with admiration; "All the guys were knocked out by her charm"
verb
Empty (as of tobacco) by knocking out; "knocked out a pipe"

Synonyms of 'knock out'

From: Moby Thesaurus