Not chemically reactive (5)
I believe the answer is:
inert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not chemically reactive</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 "(Chem.) not reactive" , "Motionless or lifeless" , "Motionless, still" , "Sluggish - unresponsive" , "Slow and apathetic" .)