immovability vs fixity

immovability and fixity both are nouns.

Word	Noun	Adjective	Verb	Adverb
immovability	Yes	No	No	No
fixity	Yes	No	No	No

As nouns, fixity is a hyponym of immovability; that is, fixity is a word with a more specific, narrower meaning than immovability:

Other hyponyms of immovability include tautness, tightness, fastness, fixedness, fixture, secureness, firmness, steadiness.

immovability (noun)	fixity (noun)
not capable of being moved or rearranged	the quality of being fixed in place as by some firm attachment
	the quality of being incapable of mutation