immutability vs unchangeability

immutability and unchangeability both are nouns.

Word	Noun	Adjective	Verb	Adverb
immutability	Yes	No	No	No
unchangeability	Yes	No	No	No

As nouns, unchangeability is a hypernym of immutability; that is, unchangeability is a word with a broader meaning than immutability:

immutability: the quality of being incapable of mutation
unchangeability: the quality of being unchangeable; having a marked tendency to remain unchanged

Other hypernyms of immutability include changelessness, unchangeableness, unchangingness.

immutability (noun)	unchangeability (noun)
the quality of being incapable of mutation	the quality of being unchangeable; having a marked tendency to remain unchanged