By the sound of it, trim couple (4)
I believe the answer is:
pair
'couple' is the definition.
('pair' can be a synonym of 'couple')
'by the sound of it trim' is the wordplay.
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'trim' becomes 'pare' (I've seen this before).
'pare' sounds like 'PAIR'.
(Other definitions for pair that I've seen before include "Put together - two of a kind" , "Twins" , "Two ducks in one game of cricket" , "Agreement to avoid division" , "players of duet?" .)