The Oxford Thesaurus An A-Z Dictionary of Synonyms - inactivityn.

1) passiveness or passivity, placidity or placidness, quiet, tranquillity, serenity, peace, peacefulness; motionlessness, immobility, stillness, inertia, inertness, lifelessness, sluggishness, listlessness, lethargy, languidness, indolence, laziness, torpor, somnolence, idleness, slothfulness, sloth: She alternates between periods of activity and inactivity. 2) inaction, quiescence; hibernation, aestivation: During repairs, the reactor will be in a state of inactivity. Some animals have a period of inactivity during certain times of the year.