Powerlessness (9)
(Other definitions for impotence that I've seen before include "Weakness" , "ineffectualness" , "Helplessness, powerlessness" .)
'powerlessness' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for inability that I've seen before include "Lack of knack!" , "Lack of sufficient power or means" , "Powerlessness" , "Lack of capacity for action" , "Impotence, incapacity" .)