Trim couple, by the sound of it
I believe the answer is:
pare
'trim' is the definition.
(I know that trim can be written as pare)
'couple by the sound of it' is the wordplay.
'couple' becomes 'pair' (synonyms).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'pair' sounds like 'PARE'.
(Other definitions for pare that I've seen before include "Trim by slicing" , "Shave or peel" , "Trim by cutting" , "Whittle" , "Shave, say, pencil" .)