Cosmos; an anaesthetic (5)
I believe the answer is:
ether
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cosmos</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">an anaesthetic</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(ether is a kind of anaesthetic)</span><br/ ><br/ ></span>
(Other definitions for ether that I've seen before include "An early anaesthetic" , "Rare atmosphere" , "Type of chemical" , "Old anaesthetic -- three (anag)" , "Anaesthetic is, strangely, there" .)