Be leaving, accepting direction (5)
I believe the answer is:
exist
'be' is the definition.
('exist' can be a synonym of 'be')
'leaving accepting direction' is the wordplay.
'leaving' becomes 'exit' (exit is a kind of leaving).
'accepting' means one lot of letters goes inside another.
'direction' becomes 's' (S is an example).
'exit' placed around 's' is 'EXIST'.
(Other definitions for exist that I've seen before include "Have objective reality" , "Subsist" , "quick!" , "Live" , "Survive" .)