Cutting rotten carcass with it (9)
I believe the answer is:
sarcastic
'cutting' is the definition.
(thesaurus)
'rotten carcass with it' is the wordplay.
'rotten' is an anagram indicator.
'with' is a charade indicator (letters next to each other).
'carcass' put after 'it' is 'itcarcass'.
'itcarcass' anagrammed gives 'SARCASTIC'.
(Other definitions for sarcastic that I've seen before include "Using biting irony" , "Expressing ridicule, contempt, maybe irony" , "Ironically mocking" , "Using mocking wit" , "Bitingly ironic" .)