a.

1. 擊倒對手的
2. 淘汰的
3. 【口】給人深刻印象的

n.

1. （拳擊）擊倒；判敗擊倒
   His new girlfriend is a real knockout.

   他的新女友實在很動人。

2. 淘汰賽
3. 【口】給人留下深刻印象的人（或物）

n.

1. an act of knocking someone out.
2. Brit. a tournament in which the loser in each round is eliminated.
3. informal an extremely attractive or impressive person or thing.