Source : Webster's Revised Unabridged Dictionary (1913)

Incontestable \In`con*test"a*ble\, a. [Pref. in- not +
   contestable: cf. F. incontestable.]
   Not contestable; not to be disputed; that cannot be called in
   question or controverted; incontrovertible; indisputable; as,
   incontestable evidence, truth, or facts. --Locke.

   Syn: Incontrovertible; indisputable; irrefragable;
        undeniable; unquestionable; intuitable; certain. --
        {In`con*test"a*ble*ness}, n. -- {In`con*test"a*bly},
        adv.

Source : WordNet®

incontestable
     adj 1: incapable of being contested or disputed [syn: {incontestible}]
            [ant: {contestable}]
     2: not open to question; obviously true; "undeniable guilt";
        "indisputable evidence of a witness" [syn: {indisputable},
         {undisputable}]