Leave be, with no end of mess (4)
I believe the answer is:
exit
'leave' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for exit that I've seen before include "Actor's departure" , "Departure of actor" , "Act of going out" , "Sudden rush of pleasure" , "Relinquish the lead" .)