Scathingly sarcastic (7)
I believe the answer is:
caustic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">scathingly sarcastic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for caustic that I've seen before include "Burning, corroding" , "Chemically burning" , "Severe" , "Burning - cutting" , "Biting (wit); burning" .)