What is the meaning of Sullen?

Having a brooding ill temper; sulky.

Gloomy; dismal; foreboding.

Sluggish; slow.

Lonely; solitary; desolate.

Mischievous; malignant; unpropitious.

Obstinate; intractable.

One who is solitary, or lives alone; a hermit.

Sullen feelings or manners; sulks; moroseness.

To make sullen.

must, to have to

may, be allowed to

will, shall, be going to (future tense)

to be about to (inchoative)

indicates a possible or hypothetical situation

indicates information garnered from a third party that may or may not be reliable

Alternative form of sellen

first-person singular past indicative of suollit

Source: wiktionary.org