Deny criminal brute (5)
I believe the answer is:
rebut
'deny' is the definition.
(thesaurus)
'criminal brute' is the wordplay.
'criminal' indicates an anagram.
'brute' is an anagram of 'REBUT'.
(Other definitions for rebut that I've seen before include "Give the lie to" , "Refure or disprove" , "show as bad" , "Prove the claim wrong" , "Tuber (anag.)" .)