Item put on behind silks? (6)
I believe the answer is:
briefs
This clue is a double definition.
'item put on behind' is the first definition.
(briefs cover the buttocks)
'silks?' is the second definition.
(both are informal terms for lawyers)
(Other definitions for briefs that I've seen before include "Close-fitting underpants" , "Instructs a barrister" , "small underwear" , "Underpants for lawyers?" , "Barristers' cases or advices" .)