Unit of weight of silk (6)
I believe the answer is:
denier
'unit of weight of silk' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for denier that I've seen before include "One who doesn't believe" , "Unit of weight for fine material, silk or nylon" , "One refusing to admit" , "Conspiracist probably" , "Peter?" .)