Synonyms for Glum (same or very similar meaning)
WordNet sense 1 (showing a brooding ill humor):
dark, dour, glowering, moody, morose, saturnine, sour, sullenWordNet sense 2 (having an irritable and unpleasant disposition):
ill-naturedWordNet sense 3 (reflecting gloom):
gloomy, long-facedWordNet sense 4 (affected or marked by low spirits):
dejectedFrom the ODE community, based on WordNetadd/edit