Inertia (9)
I believe the answer is:
lassitude
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">inertia</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for lassitude that I've seen before include "Listlessness, fatigue" , "30 [LETHARGY]" , "Weakness" , "Listlessness, state of apathy" , "Is saluted with tiredness" .)