Upper atmosphere (5)
I believe the answer is:
ether
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">upper atmosphere</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 ether that I've seen before include "Colourless volatile highly inflammable liquid" , "Old anaesthetic -- three (anag)" , "Highly flammable liquid once used as an anaesthetic" , "Light liquid used as anaesthetic" , "Solvent; clear sky (poet.)" .)