Lots of cotton socks (4)
I believe the answer is:
tons
'lots' is the definition.
('tons' can be a synonym of 'lots')
'of cotton socks' is the wordplay.
'of' says the answer is hidden in the clue.
'TONS' is hidden in the letters of 'cotton socks'.
(Other definitions for tons that I've seen before include "Each is equivalent to 2240 pounds" , "Lots" , "Loads (sl.)" , "A lot" .)