(n.) The quality or state of being placid; calmness; serenity.

accidia acedia aloofness apathy ataraxia benumbedness blah blahs bovinity calmness carelessness casualness comatoseness composure contemplation coolness detachment disinterest dispassion dispassionateness disregard disregardfulness dullness easy temper easygoingness even temper good temper heartlessness hebetude heedlessness hopelessness impassiveness impassivity imperturbability imperturbableness inappetence inattention incuriosity indifference indiscrimination inexcitability inexcitableness inirritability insouciance lack of affect lack of appetite lackadaisicalness languidness lethargicalness lethargy listlessness lucid stillness marmoreal repose mindlessness negligence nirvana nonchalance numbness passiveness passivity patience peace peacefulness phlegm phlegmaticalness phlegmaticness placidity placidness plucklessness pococurantism quiescence quiescency quiet quietism quietness quietude recklessness regardlessness repose resignation resignedness rest restfulness sangfroid satori serenity silence silken repose sleep sloth sluggishness slumber smooth temper sopor soporifousness spiritlessness spunklessness steadiness stillness stoicism stolidity stupefaction stupor supineness torpidity torpidness torpor tranquillity unanxiousness unconcern unirritableness unmindfulness unnervousness unpassionateness unsolicitousness wise passiveness withdrawnness