Phrasal verbs are multi-word verbs that, like single-word verbs, convey action of the body or mind or occurrences. Phrasal verbs consist of a basic verb + another word or words, usually a preposition or adverb. Example: speak (basic verb) + up (preposition)
set something off
Meaning / Example:
1. to ignite something, such as fireworks. > The boys were setting firecrackers off all afternoon. > They set off rocket after rocket.
2. to cause something to begin. > The coach set the race off with a shot from the starting pistol.
3. to make something distinct or outstanding. > The lovely stonework sets the fireplace off quite nicely.