Bush sounds stupid (4)
I believe the answer is:
sloe
'bush' is the definition.
(sloe is a kind of bush)
'sounds stupid' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'stupid' becomes 'slow' ('slow' can be similar in meaning to 'stupid').
'slow' sounds like 'SLOE'.
(Other definitions for sloe that I've seen before include "Fruit steeped in gin to make a liqueur" , "Sour blue-black fruit" , "Wild plum" , "Thorny bush with plum-like fruit" , "Black fruit" .)