means Sullenly gloomy and ill-tempered, sunk in a sadness that won't be coaxed out of it.

from From Latin morosus, 'peevish, fussy, set in one's ways,' which itself grew from mos (genitive moris), meaning 'manner, habit, will' — the same root that gives us 'moral' and 'morality.' The thread of meaning is telling: a morose person is, etymologically, someone ruled by their own stubborn temper, locked into a mood by sheer force of habit. It entered English in the 16th century carrying that flavor of self-willed sourness.