Idleness (7)

I believe the answer is:
inertia
'idleness' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for inertia that I've seen before include "Slowness to take action, state of laziness" , "Immobility" , "Apathetic state" , "Motion (if any) when no external force is applied" , "Slowness to act, lassitude" .)