Burning; sarcastic (7)
I believe the answer is:
caustic
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">burning</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">sarcastic</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for caustic that I've seen before include "Scathing" , "Burning, corrosive" , "Burning - cutting" , "Corrosive - cutting" , "Acrimonious - sarcastic" .)