to cause an activity or event, often a series of events, to begin or happen

The court's initial verdict in the police officers' trial set off serious riots. 法庭审理这起警官案件作出的初审判决引起了严重的暴乱。

to cause a loud noise or explosion, such as that made by a bomb or an alarm (= a warning sound) to begin or happen

Terrorists set off a bomb in the city centre. 恐怖分子在市中心引爆了一颗炸弹。

Somebody set the alarm off on my car. 有人触发了我车上的报警器。

to make something look attractive by providing a contrast (= attractive difference) to it

The new yellow cushions nicely set off the pale green of the chair covers. 黄色的新靠垫把浅绿色的椅套衬托得很好看。

to cause someone to start doing something

[ + -ing verb ] Every time I think about it, it sets me off laughing. 每次我想到它，就会笑起来。

She's finally stopped crying - don't set her off again. 她终于不哭了——现在别再惹她哭了。