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The Collaborative International Dictionary
Incommensurableness

Incommensurable \In`com*men"su*ra*ble\, a. [Pref. in- not + commensurable: cf. F. incommensurable.] Not commensurable; having no common measure or standard of comparison; as, quantities are incommensurable when no third quantity can be found that is an aliquot part of both; the side and diagonal of a square are incommensurable with each other; the diameter and circumference of a circle are incommensurable.

They are quantities incommensurable.
--Burke. -- In`com*men"su*ra*ble*ness, n. -- In`com*men"su*ra*bly, adv.

Wiktionary
incommensurableness

n. (context rare English) incommensurability.