Sailor's trousers (4-7)
I believe the answer is:
bell-bottoms
'sailor's trousers' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for bell-bottoms that I've seen before include "Flared trousers" , "Naval rating's trousers" , "Wide-flared trousers" , "Trousers with a flare below the knee" , "Sailor's trousers" .)