disability vs unfitness

disability and unfitness both are nouns.

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

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

disability: the condition of being unable to perform as a consequence of physical or mental unfitness
unfitness: poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)

Other hypernyms of disability include softness.

disability (noun)	unfitness (noun)
the condition of being unable to perform as a consequence of physical or mental unfitness	the quality of not being suitable
	lacking the power to perform
	poor physical condition; being out of shape or out of condition (as from a life of ease and luxury)