mordant vs grim

mordant is a noun but grim is not a noun.

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

As adjectives, mordant and grim are synonyms defined as:

Other synonyms of mordant include black.

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

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