Boutonniere site (5)
I believe the answer is:
lapel
'boutonniere site' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lapel that I've seen before include "Feature of a jacket" , "Fold of coat" , "Continuation of a coat collar" , "Part of a folded back collar" , "Jacket fold" .)