Denis, stupidly supercilious (5)
I believe the answer is:
snide
'supercilious' is the definition.
(synonyms)
'denis stupidly' is the wordplay.
'stupidly' indicates anagramming the letters (a stupid ordering of the letters).
'denis' is an anagram of 'SNIDE'.
(Other definitions for snide that I've seen before include "Indirectly mocking" , "Derogatory in an insinuating way" , "Derogatory, sneering" , "Derogatory, showing malice" , "Supercilious, malicious" .)