grim

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

• adjective Discouraging or depressing.
• adjective Dismal; gloomy.
• adjective Stern or forbidding.
• adjective Repellent or horrifying: synonym: ghastly.
• adjective Unrelenting or uncompromising.

from The Century Dictionary.

• Of a fierce, stern, or forbidding aspect; severe or repellent in appearance or demeanor; fierce; sullen; surly.
• Stern in character or quality; unyielding; dreadful; formidable: as, grim determination.
• Marked by harshness or severity; distressful; dolorous; cheerless: as, grim suffering; a grim jest.
• Synonyms Grisly, Hideous, etc. (see ghastly); severe, harsh, hard.
• noun Anger; wrath.
• To make grim; give a stern or forbidding aspect to.

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

• adjective Of forbidding or fear-inspiring aspect; fierce; stern; surly; cruel; frightful; horrible.

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

• adjective dismal and gloomy, cold and forbidding
• adjective rigid and unrelenting
• adjective ghastly or sinister
• adjective UK, slang disgusting; gross

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

• adjective causing dejection
• adjective not to be placated or appeased or moved by entreaty
• adjective filled with melancholy and despondency
• adjective harshly ironic or sinister
• adjective shockingly repellent; inspiring horror
• adjective harshly uninviting or formidable in manner or appearance