Bully with endless scowl (3)
I believe the answer is:
cow
'bully' is the definition.
(I've seen this before)
'with endless scowl' is the wordplay.
'with' indicates a hidden word.
'COW' is hidden within 'endless scowl'.
(Other definitions for cow that I've seen before include "Frighten with intimidations" , "cause fear" , "Overawe" , "Intimidate; an animal" , "Female farm animal" .)