knockout
US /ˈnɑːk.aʊt/
UK /ˈnɑːk.aʊt/

1.
a blow that renders an opponent unconscious
:
•
The boxer delivered a powerful knockout punch.
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It was a clean knockout in the first round.
2.
a very attractive or impressive person or thing
:
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She looked like a real knockout in her new dress.
•
That car is a total knockout.
1.
causing an opponent to be unconscious
:
•
He delivered a knockout punch.
•
The drug has a knockout effect on pain.