sullen in WordNet English dictionary

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"
   dark  dour  glowering  glum  moody  morose  saturnine  sour  sullen 
   
2. darkened by clouds
   "a heavy sky"
   heavy  lowering  sullen  threatening