Sarcastic, cutting (7)
I believe the answer is:
caustic
This clue is a double definition.
'sarcastic' is the first definition.
(thesaurus)
'cutting' is the second definition.
(I've seen this before)
(Other definitions for caustic that I've seen before include "Harsh or corrosive" , "Able to burn - cutting" , "Severe" , "Acrid" , "Chemically burning" .)