Complement of socks (4)
I believe the answer is:
pair
'complement of socks' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pair that I've seen before include "Duo" , "flight of stairs" , "E.g. two aces; mate" , "Set of two" , "Two ducks in one game of cricket" .)