Frozen carbon dioxide (3,3)
I believe the answer is:
dry ice
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">frozen carbon dioxide</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for dry ice that I've seen before include "Solidified CO2" , "Theatrical mist" , "Carbon dioxide snow" , "Carbon dioxide vapour used on stage" , "Producer of stage mist" .)