Use sound trees (4)
I believe the answer is:
yews
'trees' is the definition.
(yew is a kind of tree)
'use sound' is the wordplay.
'sound' indicates a 'sounds like' (homophone) clue.
'use' sounds like 'YEWS'.
(Other definitions for yews that I've seen before include "Evergreen trees" , "woods" , "traditional churchyard residents" .)