Definitions:

1. cause to burst with a violent release of energy verb
   • The kids set off rockets on the 4th of July.
2. leave where one is verb
   • I set off for London by foot with two quid and a biscuit.
3. provoke or stir up verb
   • The use of tear gas set off the protesters.
4. set in motion or cause to begin verb
   • Mixing Chlorine with Ammonia sets off a dangerous reaction.

Synonyms:

• blow up
• bring out
• incite
• instigate
• offset
• start
• stir up
• trip