Chain for a pocket watch (3)
I believe the answer is:
fob
'chain for a pocket watch' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for fob that I've seen before include "Chain for a pocket watch" , "Chain attached to watch" , "Small watch pocket" , "Waistcoat pocket" , "Kind of watch on a chain" .)