Not quick to react (5)
I believe the answer is:
inert
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not quick to react</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 "Devoid of motion or change" , "Like some gases" , "Slow and apathetic" , "(Chem.) not reactive" , "Unreactive; still" .)