unforgiving vs relentless

unforgiving and relentless both are adjectives.

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

As adjectives, unforgiving and relentless are synonyms defined as:

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

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

unforgiving (adjective)	relentless (adjective)
unwilling or unable to forgive or show mercy	never-ceasing
not to be placated or appeased or moved by entreaty	not to be placated or appeased or moved by entreaty