Avoid rear-end collision, for the most part (4)
I believe the answer is:
shun
'avoid' is the definition.
(I know that shun is a more specific form of the action avoid)
'rear-end collision for the most part' is the wordplay.
'rear end collision' becomes 'shunt' (I've seen this before).
'for the most part' means to remove the last letter (most but not all of the letters).
'shunt' with its final letter taken away is 'SHUN'.
(Other definitions for shun that I've seen before include "Keep away from Huns" , "Avoid, ignore" , "Persistently avoid" , "attention in the army" , "Deliberately have no contact with" .)