Chemically inactive (5)
I believe the answer is:
inert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">chemically inactive</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 inert that I've seen before include "Incapable of acting, like some gas" , "Sluggish - unresponsive" , "Like e.g. xenon" , "Chemically unreactive" , "Sluggish, inactive" .)