Lack of movement (10)
'lack of movement' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for inaction that I've seen before include "Dormancy" , "Idleness - fighting" , "Inertia" , "Immobility" , "Lethargy -- not in CIA (anag)" .)
(Other definitions for stagnation that I've seen before include "Lack of activity" , "State of little activity" , "movement's antithesis?" , "It's still" , "standstill" .)