The Collaborative International Dictionary of English v.0.48:

Inaction \In*ac"tion\, n. [Pref. in. not + action: cf.
   inaction.]
   Lack of action or activity; forbearance from labor; idleness;
   rest; inertness. --Berkeley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inaction
    n 1: the state of being inactive [syn: inaction, inactivity,
         inactiveness] [ant: action, activeness, activity]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "inaction":
   dormancy, drift, fixation, fixity, hibernation, idleness,
   immobility, inactiveness, inactivity, indolence, inertia,
   inertness, lethargy, lull, motionlessness, quiescence, slackness,
   slothfulness, suspension, torpidity, underactivity