Inertia (9)
I believe the answer is:
lassitude
'inertia' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for lassitude that I've seen before include "Listlessness, fatigue" , "30 [LETHARGY]" , "Weakness" , "Listlessness, state of apathy" , "Is saluted with tiredness" .)