unfit vs unfitness

unfit is not a noun while unfitness is a noun.

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

unfit (noun)	unfitness (noun)
	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)

unfit (adjective)	unfitness (adjective)
not in good physical or mental condition; out of condition
below the required standards for a purpose
physically unsound or diseased

unfit (verb)	unfitness (verb)
make unfit or unsuitable