To set off is to begin a journey. Bags in the car, and away.
It is the standard British phrase for departing, and setting off early is what everybody promises and nobody does. There is a quite separate sense meaning to trigger, since setting off an alarm, a firework or a chain of events all mean starting something suddenly. A third sense is about contrast, and a colour that sets off another displays it well. Set out means much the same as the first sense.
1phraseset offTo begin a journey.
“We should set off before the traffic builds.”
2phrasecauseTo cause something to start suddenly.
“The smoke will set off the alarm.”
Also accepted in games: set out
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 4 of A Man Called Ove.
Practise this word