Set off, getting boxed in on return with not enough parking (6)
I believe the answer is:
depart
'set off' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(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.)" .)