What does "incommensurable" mean?

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.