grim vs mordant

grim is not a noun while mordant is a noun.

Word	Noun	Adjective	Verb	Adverb
grim	No	Yes	No	No
mordant	Yes	Yes	No	No

As adjectives, grim and mordant are synonyms defined as:

Other synonyms of grim include black.

grim (noun)	mordant (noun)
	a substance used to treat leather or other materials before dyeing; aids in dyeing process

grim (adjective)	mordant (adjective)
shockingly repellent; inspiring horror	of a substance, especially a strong acid; capable of destroying or eating away by chemical action
filled with melancholy and despondency	harshly ironic or sinister
causing dejection
not to be placated or appeased or moved by entreaty
harshly ironic or sinister
harshly uninviting or formidable in manner or appearance