Morose

Etymology

From Latin morosus, "peevish, hard to please," which grew out of mos (genitive moris), "manner, custom, self-will" — the same root as "moral." The original idea was a person ruled by their own rigid moods and whims, hence "fretful." English narrowed that to today’s sense of gloomy, sulking ill temper.

adjective · /muh-ROHS/
Sullen, gloomy, and ill-humored, often in a withdrawn and brooding way.
What it names
The mood of someone who has retreated into their own dark cloud and answers the world in monosyllables.
Example
He turned morose after the news, sitting apart from the celebration and staring into his drink.
Related idea
Sullen implies a resentful, silent refusal to engage; morose leans more toward heavy, depressive gloom than active grievance.