unalterability vs unalterable

unalterability is a noun but unalterable is not a noun.

Word	Noun	Adjective	Verb	Adverb
unalterability	Yes	No	No	No
unalterable	No	Yes	No	No

unalterability (noun)	unalterable (noun)
the quality of not being alterable
the quality of being fixed and unchangeable

unalterability (adjective)	unalterable (adjective)
	not capable of being changed or altered
	of a sentence; that cannot be changed
	remaining the same for indefinitely long times