Like argon (5)
I believe the answer is:
inert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">like argon</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 inert that I've seen before include "dead" , "lacking energy" , "like neon" , "Passive, immobile" , "Lifeless; apathetic" .)