Car part, left out for scrap (3)
I believe the answer is:
axe
'scrap' is the definition.
(both can mean to cancel or fire)
'car part left out' is the wordplay.
'car part' becomes 'axle' (part of a car).
'left' becomes 'L' (common abbreviation).
'out' is a deletion indicator.
'axle' with 'l' taken out is 'AXE'.
'for' is the link.
(Other definitions for axe that I've seen before include "Fire weapon" , "Abandon project with chopping tool" , "Guitar" , "Chop" , "Chopping tool; dismiss" .)