Pronunciation: (som'bur),[key] —adj. 1. gloomily dark; shadowy; dimly lighted: a somber passageway. 2. dark and dull, as color, or as things in respect to color: a somber dress. 3. gloomy, depressing, or dismal: a somber mood. 4. extremely serious; grave: a somber expression on his face.Also,esp. Brit.,som'bre.