Princeton's WordNet

1. grim, inexorable, relentless, stern, unappeasable, unforgiving, unrelenting(adj)

   not to be placated or appeased or moved by entreaty

   "grim determination"; "grim necessity"; "Russia's final hour, it seemed, approached with inexorable certainty"; "relentless persecution"; "the stern demands of parenthood"

2. ghastly, grim, grisly, gruesome, macabre, sick(adj)

   shockingly repellent; inspiring horror

   "ghastly wounds"; "the grim aftermath of the bombing"; "the grim task of burying the victims"; "a grisly murder"; "gruesome evidence of human sacrifice"; "macabre tales of war and plague in the Middle ages"; "macabre tortures conceived by madmen"

3. black, grim, mordant(adj)

   harshly ironic or sinister

   "black humor"; "a grim joke"; "grim laughter"; "fun ranging from slapstick clowning ... to savage mordant wit"

4. dour, forbidding, grim(adj)

   harshly uninviting or formidable in manner or appearance

   "a dour, self-sacrificing life"; "a forbidding scowl"; "a grim man loving duty more than humanity"; "undoubtedly the grimmest part of him was his iron claw"- J.M.Barrie

5. gloomy, grim, blue, depressed, dispirited, down(p), downcast, downhearted, down in the mouth, low, low-spirited(adj)

   filled with melancholy and despondency

   "gloomy at the thought of what he had to face"; "gloomy predictions"; "a gloomy silence"; "took a grim view of the economy"; "the darkening mood"; "lonely and blue in a strange city"; "depressed by the loss of his job"; "a dispirited and resigned expression on her face"; "downcast after his defeat"; "feeling discouraged and downhearted"

6. blue, dark, dingy, disconsolate, dismal, gloomy, grim, sorry, drab, drear, dreary(adj)

   causing dejection

   "a blue day"; "the dark days of the war"; "a week of rainy depressing weather"; "a disconsolate winter landscape"; "the first dismal dispiriting days of November"; "a dark gloomy day"; "grim rainy weather"

Kernerman English Learner's Dictionary

1. grim(adjective)ɪm

   depressing and without hope

   a grim picture of the future; the grim truth

2. grimɪm

   (of a place) unattractive and boring

   a grim town

3. grimɪm

   looking worried or depressed

   a grim expression

Wiktionary

1. grim(Adjective)

   dismal and gloomy, cold and forbidding

2. grim(Adjective)

   rigid and unrelenting

3. grim(Adjective)

   ghastly or sinister

4. Grim(ProperNoun)

   , probably derived from Old English grimm or Old Norse grimr or grimmr.

Origin: From grim.

Webster Dictionary

1. Grim

   of forbidding or fear-inspiring aspect; fierce; stern; surly; cruel; frightful; horrible

• grimmige, wredeAfrikaans
• كَريه، مُثير للإشْمِئْزازArabic
• зловещBulgarian
• terrívelPortuguese (BR)
• příšerný, neradostnýCzech
• schrecklichGerman
• grusom; barskDanish
• φρικτός, δυσάρεστοςGreek
• horrible, horroroso, macabro, nefastoSpanish
• peletavEstonian
• دلخراش؛ ناخوشایندFarsi
• epämiellyttäväFinnish
• sinistreFrench
• נוֹרָאִיHebrew
• भयानकHindi
• strašan, turobanCroatian
• félelmetesHungarian
• mengerikanIndonesian
• andstyggilegur,óhugnanlegurIcelandic
• macabroItalian
• ぞっとするようなJapanese
• 무서운Korean
• siaubingas, bjaurus, atgrasusLithuanian
• drūms; briesmīgsLatvian
• susahMalay
• vreselijk; akeligDutch
• forferdelig, nifs, uhyggeligNorwegian
• ponuryPolish
• دلخراش؛ ناخوشایندPersian
• بیروونکیPashto
• macabroPortuguese
• sinistruRomanian
• неприятныйRussian
• ponurý, strašnýSlovak
• zoprnSlovenian
• sumoranSerbian
• ohyggligSwedish
• ร้ายกาจThai
• korkunçTurkish
• 令人害怕的, 令人極不愉快的Chinese (Trad.)
• жорстокийUkrainian
• خشمگیںUrdu
• khốc liệtVietnamese
• 令人害怕的，讨厌的Chinese (Simp.)