Set off

What is Set off ?

Set off is (verb) 1. to begin a trip We’re setting off for Germany tomorrow. They all set off on a long walk after lunch. 2. to start something happening They set off a bomb in the shopping centre. If you touch the wire it will set off the alarm. Being in the same room as a cat will set off my asthma.

 

source: Easier English, Student Dictionary Upper Intermediate Level