1. 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. 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. harshly ironic or sinister;

"black humor"

"a grim joke"

"grim laughter"

"fun ranging from slapstick clowning ... to savage mordant wit"

4. 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"

5. 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

6. characterized by hopelessness; filled with gloom;

"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"