relentless vs grim

relentless and grim both are adjectives.

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

As adjectives, relentless and grim are synonyms defined as:

relentless and grim: not to be placated or appeased or moved by entreaty

Other synonyms of relentless include inexorable, stern, unappeasable, unforgiving, unrelenting.

relentless (adjective)	grim (adjective)
never-ceasing	shockingly repellent; inspiring horror
not to be placated or appeased or moved by entreaty	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