frailty vs unfitness

frailty and unfitness both are nouns.

Word	Noun	Adjective	Verb	Adverb
frailty	Yes	No	No	No
unfitness	Yes	No	No	No

As nouns, unfitness is a hypernym of frailty; that is, unfitness is a word with a broader meaning than frailty:

frailty: the state of being weak in health or body (especially from old age)
unfitness: poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)

Other hypernyms of frailty include softness.

frailty (noun)	unfitness (noun)
moral weakness	the quality of not being suitable
the state of being weak in health or body (especially from old age)	lacking the power to perform
	poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)