Buttonhole constituent on the way back (4)
I believe the answer is:
trap
'buttonhole' is the definition.
(I know that buttonhole is a more specific form of the action the trap)
'constituent on the way back' is the wordplay.
'constituent' becomes 'part' (a part is a constituent of something).
'on the way back' shows that the letters should be reversed in order.
'part' in reverse letter order is 'TRAP'.
(Other definitions for trap that I've seen before include "that can let an actor down" , "Part (anag.)" , "Cakehole (slang)" , "Ambush" , "ladder" .)