Incomplete back lapel (6)
I believe the answer is:
revers
'lapel' is the definition.
(revers is a kind of lapel)
'incomplete back' is the wordplay.
'incomplete' means to remove the last letter.
'back' becomes 'reverse' (I've seen this before).
'reverse' with its last letter taken off is 'REVERS'.
(Other definitions for revers that I've seen before include "One turns back" , "Part of garment" , "Lining" , "a turn-up for the cloth?" .)