Set off, getting boxed in on return with not enough parking (6)

I believe the answer is:

depart

I'm a little stuck... Click here to teach me more about this clue!

'set off' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for depart that I've seen before include "Leave (6)" , "Take one's leave, go" , "Go away or leave" , "Clearly expressive" , "Prated (anag.)" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app