gloom

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Partial or total darkness; dimness.
• noun A partially or totally dark place, area, or location.
• noun An atmosphere of melancholy or depression.
• noun A state of melancholy or depression; despondency.
• intransitive verb To be or become dark, shaded, or obscure.
• intransitive verb To feel, appear, or act despondent, sad, or mournful.
• intransitive verb To make dark, shaded, or obscure.
• intransitive verb Archaic To make despondent; sadden.

from The Century Dictionary.

• To appear dimly; be seen in an imperfect or waning light; glimmer; be in darkness or obscurity.
• To exhibit or produce a somber or melancholy feeling; appear sad, gloomy, or dismal; frown; lower.
• To darken, or make dark, gloomy, or somber.
• To fill with gloom or despondency; make gloomy or sad.
• noun Dim, glimmering shade; deep twilight; cheerless obscurity; darkness: as, the gloom of a forest.
• noun Hence — A dark place.
• noun Cloudiness or heaviness of mind; dejection, melancholy, sullenness, and the like, or an aspect indicative of such feelings.
• noun A depressing or disheartening condition of affairs; a dismal aspect or prospect.
• noun In gunpowder-manuf., the drying-oven.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To shine or appear obscurely or imperfectly; to glimmer.
• intransitive verb To become dark or dim; to be or appear dismal, gloomy, or sad; to come to the evening twilight.
• noun Partial or total darkness; thick shade; obscurity.
• noun A shady, gloomy, or dark place or grove.
• noun Cloudiness or heaviness of mind; melancholy; aspect of sorrow; low spirits; dullness.
• noun In gunpowder manufacture, the drying oven.
• transitive verb To render gloomy or dark; to obscure; to darken.
• transitive verb To fill with gloom; to make sad, dismal, or sullen.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun darkness, dimness or obscurity.
• noun a melancholy, depressing or despondent atmosphere
• verb intransitive To be dark or gloomy.
• verb intransitive to look or feel sad, sullen or despondent.
• verb transitive To render gloomy or dark; to obscure; to darken.
• verb transitive To fill with gloom; to make sad, dismal, or sullen.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a state of partial or total darkness
• noun a feeling of melancholy apprehension
• noun an atmosphere of depression and melancholy