Ox boxed in by prize bull (4)
I believe the answer is:
zebu
'ox' is the definition.
(thesaurus)
'boxed in by prize bull' is the wordplay.
'boxed in' says the answer is hidden in the clue.
'ZEBU' is hidden in the letters of 'by prize bull'.
(Other definitions for zebu that I've seen before include "cattle" , "Bovine animal" , "Humped ox domesticated in India" , "Asian ox" , "Type of ox" .)