Source : WordNet®

inactiveness
     n 1: the state of being inactive [syn: {inaction}, {inactivity}]
          [ant: {action}, {action}, {action}]
     2: a state of no activity [syn: {inaction}]
     3: a disposition to remain inactive or inert; "he had to
        overcome his inertia and get back to work" [syn: {inactivity},
         {inertia}] [ant: {activeness}]