to begin a journey We set off for London just after ten.
- 1 to make a bomb, etc. explode A gang of boys were setting off fireworks in the street.
- 2 to make an alarm start ringing Opening this door will set off the alarm.
- 3 to start a process or series of events Panic on the stock market set off a wave of selling.
- 4to make something more noticeable or attractive by being placed near it That blouse sets off the blue of her eyes.