Carnage or dreadful self-importance (9)
I believe the answer is:
arrogance
'self-importance' is the definition.
(I've seen this before)
'carnage or dreadful' is the wordplay.
'dreadful' indicates an anagram.
'carnage'+'or'='carnageor'
'carnageor' with letters rearranged gives 'ARROGANCE'.
(Other definitions for arrogance that I've seen before include "Wild self-importance" , "disdain" , "Overbearing attitude of pride and insolence" , "Conceit, self-importance" , "Conceitedness" .)