set off phrasal verb ( see also ↑ set )
1 . to start to go somewhere:
I’ll set off early to avoid the traffic.
set off for
Jerry and I set off on foot for the beach.
2 . set something ↔ off to make something start happening, especially when you do not intend to do so:
News that the claims might be true set off widespread panic.
Hong Kong’s stock market fell, setting off a global financial crisis.
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In written English, people often say that something triggers a particular reaction or event, rather than sets it off , because it sounds more formal:
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This could trigger a global financial crisis.
3 . set something ↔ off to make an ↑ alarm start ringing:
Smoke from a cigarette will not normally set off a smoke alarm.
4 . set something ↔ off to make a bomb explode, or cause an explosion:
Any movement could have set off the bomb.
5 . set something ↔ off if a piece of clothing, colour, decoration etc sets something off, it makes it look attractive:
The blue sundress set off her long blonde hair.
6 . set somebody off to make someone start laughing, crying, or talking about something:
Don’t mention what happened – you’ll only set her off again.
7 . set something off against tax to officially record the money you have spent on something connected with your job, in order to reduce the amount of tax you have to pay:
Some expenses can be set off against tax.