As nouns,
irreplaceableness is a hyponym of
unexchangeability; that is, irreplaceableness is a
word with a more specific, narrower meaning than
unexchangeability:
unexchangeability: the quality of being incapable of exchange or interchange
irreplaceableness: the quality of being irreplaceable
Other hyponyms of unexchangeability include
incommutability.