grim (adj.)

Old English grimm "fierce, cruel, savage; severe, dire, painful," from Proto-Germanic *grimma- (source also of Old Saxon, Old Frisian, Old High German, German grimm "grim, angry, fierce," Old Norse grimmr "stern, horrible, dire," Swedish grym "fierce, furious"), from PIE *ghremno- "angry," which is perhaps imitative of the sound of rumbling thunder (compare Greek khremizein "to neigh," Old Church Slavonic vuzgrimeti "to thunder," Russian gremet' "thunder").

A weaker word now than it once was; sense of "dreary, gloomy" first recorded late 12c. It also had a verb form in Old English, grimman (class III strong verb; past tense gramm, past participle grummen), and a noun, grima "goblin, specter," perhaps also a proper name or attribute-name of a god, hence its appearance as an element in place names.

Grim reaper as a figurative phrase for "death" is attested by 1847 (the association of grim and death goes back at least to 17c.). A Middle English expression for "have recourse to harsh measures" was to wend the grim tooth (early 13c.).

grim (n.)

"spectre, bogey, haunting spirit," 1620s, from grim (adj.).

Definitions of grim

grim (adj.)
filled with melancholy and despondency;
took a grim view of the economy
Synonyms: gloomy / blue / depressed / dispirited / down / downcast / downhearted / down in the mouth / low / low-spirited
grim (adj.)
not to be placated or appeased or moved by entreaty;
grim necessity
grim determination
grim (adj.)
shockingly repellent; inspiring horror;
the grim task of burying the victims
the grim aftermath of the bombing
Synonyms: ghastly / grisly / gruesome / macabre / sick
grim (adj.)
harshly ironic or sinister;
a grim joke
grim laughter
Synonyms: black / mordant
grim (adj.)
harshly uninviting or formidable in manner or appearance; "undoubtedly the grimmest part of him was his iron claw"- J.M.Barrie;
a grim man loving duty more than humanity
Synonyms: dour / forbidding
grim (adj.)
causing dejection;
grim rainy weather
Synonyms: blue / dark / dingy / disconsolate / dismal / gloomy / sorry / drab / drear / dreary