grim in WordNet English dictionary

1. harshly ironic or sinister
   "black humor"; "a grim joke"; "grim laughter"; "fun ranging from slapstick clowning ... to savage mordant wit"
   black  grim  mordant 
   
2. 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"
   gloomy  grim  blue  depressed  dispirited  down  downcast  downhearted  down in the mouth  low  low-spirited 
   
3. 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"
   blue  dark  dingy  disconsolate  dismal  gloomy  grim  sorry  drab  drear  dreary 
   
4. 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
   dour  forbidding  grim 
   
5. 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"
   ghastly  grim  grisly  gruesome  macabre  sick 
   
6. 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"
   grim  inexorable  relentless  stern  unappeasable  unforgiving  unrelenting