I. knock ‧ out 1 /ˈnɒk-aʊt $ ˈnɑːk-/ BrE AmE noun [countable]
1 . when a ↑ boxer hits his opponent so hard that he falls down and cannot get up again:
The fight ended in a knockout.
2 . informal someone or something that is very attractive or successful:
Her dress was a knockout.
3 . a type of competition in which only the winning players or teams at each stage continue to play until there is only one winner
II. knockout 2 BrE AmE adjective informal
1 . knockout punch/blow
a) a hard hit that knocks someone down so that they cannot get up again
b) an action or event that causes defeat or failure:
High interest rates have been a knockout blow to the business.
2 . relating to a type of competition in which only the winning players or teams at each stage continue to play:
Scotland’s failure to get through the knockout stage of the competition
3 . knockout pills/drops etc ↑ pill s etc that make someone unconscious