feebleness vs unfitness

feebleness and unfitness both are nouns.

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

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

feebleness: 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 feebleness include softness.

feebleness (noun)	unfitness (noun)
the quality of lacking intensity or substance	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)