Awful massacre mostly brings contempt (7)
I believe the answer is:
sarcasm
'contempt' is the definition.
(I've seen this before)
'awful massacre mostly' is the wordplay.
'awful' indicates an anagram.
'mostly' means to remove the last letter.
'massacre' with its last letter taken off is 'massacr'.
'massacr' with letters rearranged gives 'SARCASM'.
'brings' acts as a link.
(Other definitions for sarcasm that I've seen before include "Ironic wit" , "Language expressing scorn or contempt" , "Scornful jibe" , "Wounding remark" , "Ironical expression of scorn or contempt" .)