relentless vs persistent

relentless and persistent both are adjectives.

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

As adjectives, relentless and persistent are synonyms defined as:

Other synonyms of relentless include unrelenting.

relentless (adjective)	persistent (adjective)
never-ceasing	retained; not shed
not to be placated or appeased or moved by entreaty	never-ceasing
	stubbornly unyielding
	continually recurring to the mind