Disgusting-sounding bird (4)
I believe the answer is:
fowl
'bird' is the definition.
(I know that bird can be written as fowl)
'disgusting-sounding' is the wordplay.
'disgusting' becomes 'foul' (both can mean horrible).
'sounding' shows a homophone (sound like).
'foul' is a homophone of 'FOWL'.
(Other definitions for fowl that I've seen before include "eg hen" , "Bird, maybe domestic" , "Domesticated bird" , "Cock or hen" , "eg Chicken" .)