fixedness vs unalterability

fixedness and unalterability both are nouns.

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

As nouns, fixedness and unalterability are synonyms defined as:

fixedness and unalterability: the quality of being fixed and unchangeable

fixedness (noun)	unalterability (noun)
the quality of being fixed in place as by some firm attachment	the quality of not being alterable
the quality of being fixed and unchangeable	the quality of being fixed and unchangeable
remaining in place