From WordNet (r) 3.0 (2006):
sullen
adj 1: showing a brooding ill humor; "a dark scowl"; "the
proverbially dour New England Puritan"; "a glum, hopeless
shrug"; "he sat in moody silence"; "a morose and
unsociable manner"; "a saturnine, almost misanthropic
young genius"- Bruce Bliven; "a sour temper"; "a sullen
crowd" [syn: dark, dour, glowering, glum,
moody, morose, saturnine, sour, sullen]
2: darkened by clouds; "a heavy sky" [syn: heavy, lowering,
sullen, threatening]