gloomy

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

• adjective Partially or totally dark, especially dismal and dreary.
• adjective Showing or filled with gloom.
• adjective Causing or producing gloom; depressing.
• adjective Marked by hopelessness; very pessimistic.

from The Century Dictionary.

• Thickly shaded; cheerlessly obscure; shadowy; dark; somber.
• Affected with, characterized by, or expressing gloom; wearing the aspect of sorrow; depressed or depressing; melancholy; doleful: as, a gloomy countenance; a gloomy prospect.
• Synonyms Dim, dusky, cloudy, cheerless, lowering. See darkness.

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

• adjective Imperfectly illuminated; dismal through obscurity or darkness; dusky; dim; clouded.
• adjective Affected with, or expressing, gloom; melancholy; dejected.

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

• adjective Imperfectly illuminated; dismal through obscurity or darkness; dusky; dim; clouded.
• adjective Affected with, or expressing, gloom; melancholy; dejected.

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

• adjective depressingly dark
• adjective causing dejection
• adjective filled with melancholy and despondency