buy的过去式是bought，过去分词是bought。作及物动词时意思是购买；买；获得；收买。作不及物动词时意思是买。作名词时意思是购买；便宜货。比如：

1、I bought him a drink in return for his help.

我请他喝酒以酬谢他的帮助。

2、He bought a used walkman for a song.

他买了一台旧随身听。

3、I bought a book yesterday.

我昨天买了一本书。