Neon or Freon (3)
I believe the answer is:
gas
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">neon or freon</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 gas that I've seen before include "Hydrogen, for example" , "eg Helium" , "Hydrogen or oxygen, say" , "Gossip" , "Eg, oxygen" .)