Assist with a crime (4)
I believe the answer is:
abet
'assist with a crime' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for abet that I've seen before include "Make good" , "Assist (in doing wrong?)" , "Aid and help, perhaps in crime" , "Incite, help" , "Assist criminally" .)