rhathymia
/rəˈθʌɪmɪə/noun
1 Theology. In the works of Paul Elmer More: lack of energy or attention; passivity. Now rare.
2 Psychology. In the factorial analysis of personality: a factor which predisposes a person towards light-heartedness and freedom from worry; (hence) the state or condition of being cheerful and carefree; optimism.
Origin
1920s. From ancient Greek ῥαθυμία (or ῥᾳθυμία) light-heartedness, easiness of temper, laziness, indifference from ῥάθυμος (or ῥᾴθυμος) light-hearted, easy tempered, indifferent (from ῥᾶ (or ῥᾴ) easily + θυμός spirit, temper: see thymoleptic) + -ία.