grim vs relentless

grim and relentless both are adjectives.

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

As adjectives, grim and relentless are synonyms defined as:

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

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

grim (adjective)	relentless (adjective)
shockingly repellent; inspiring horror	never-ceasing
filled with melancholy and despondency	not to be placated or appeased or moved by entreaty
causing dejection
not to be placated or appeased or moved by entreaty
harshly ironic or sinister
harshly uninviting or formidable in manner or appearance