The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         They are quantities incommensurable.     --Burke.
   -- In`com*men"su*ra*ble*ness, n. -- In`com*men"su*ra*bly,
   adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Incommensurable \In`com*men"su*ra*ble\, n.
   One of two or more quantities which have no common measure.
   [1913 Webster]

WordNet (r) 3.0 (2006):

incommensurable
    adj 1: impossible to measure or compare in value or size or
           excellence
    2: not having a common factor

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "incommensurable":
   abnormal, absurd, alien, anomalous, apart, detached, disconnected,
   discrete, disjunct, disproportionate, disrelated, dissimilar,
   dissociated, exotic, extraneous, foreign, incoherent,
   incommensurate, incomparable, incompatible, incongruous,
   inconsequent, inconsistent, inconsonant, independent, insular,
   irreconcilable, irrelative, isolated, not comparable to,
   of different orders, other, out of proportion, outlandish,
   oxymoronic, paradoxical, removed, segregate, self-contradictory,
   separate, separated, strange, unaffiliated, unallied, unassociated,
   unconnected, unlike, unrelatable, unrelated