relapse vs failure

relapse and failure both are nouns.

Word	Noun	Adjective	Verb	Adverb
relapse	Yes	No	Yes	No
failure	Yes	No	No	No

As nouns, failure is a hypernym of relapse; that is, failure is a word with a broader meaning than relapse:

relapse (noun)	failure (noun)
a failure to maintain a higher state	an act that fails
	an unexpected omission
	an event that does not accomplish its intended purpose
	a person with a record of failing; someone who loses consistently
	lack of success
	loss of ability to function normally
	inability to discharge all your debts as they come due

relapse (verb)	failure (verb)
go back to bad behavior
deteriorate in health