Leave with hesitation, therefore (4)
I believe the answer is:
ergo
'therefore' is the definition.
(I've seen this before)
'leave with hesitation' is the wordplay.
'leave' becomes 'go' (to go is to depart or leave).
'with' means one lot of letters go next to another.
'hesitation' becomes 'er' (sound made while hesitating - um, er).
'go' put after 'er' is 'ERGO'.
(Other definitions for ergo that I've seen before include "It follows" , "'Cogito, ---- sum'" , "Thus" , "Hence" , "for this reason" .)