The Collaborative International Dictionary of English v.0.48:

Indisputable \In*dis"pu*ta*ble\ (?; 277), a. [Pref. in- not +
   disputable: cf. F. indisputable.]
   Not disputable; incontrovertible; too evident to admit of
   dispute.

   Syn: Incontestable; unquestionable; incontrovertible;
        undeniable; irrefragable; certain; positive; undoubted;
        sure; infallible. -- In*dis"pu*ta*ble*ness, n. --
        In*dis"pu*ta*bly, adv.
        [1913 Webster]

WordNet (r) 3.0 (2006):

indisputable
    adj 1: not open to question; obviously true; "undeniable guilt";
           "indisputable evidence of a witness" [syn:
           incontestable, indisputable, undisputable]
    2: impossible to doubt or dispute; "indisputable (or sure)
       proof" [syn: indisputable, sure]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "indisputable":
   absolute, actual, adducible, admissible, admitting no exception,
   admitting no question, all-out, apparent, attestative, attestive,
   authentic, based on, beyond doubt, categorical, certain,
   circumstantial, clear, clear as crystal, complete, conclusive,
   confirmable, convincing, crystal-clear, cumulative, damning,
   decided, decisive, definite, definitive, demonstrable,
   demonstratable, determinate, determinative, discernible, distinct,
   documentary, documented, downright, entire, evident, evidential,
   evidentiary, ex parte, explicit, express, eye-witness, factual,
   final, firsthand, fixed, flat, flat-out, founded on, global,
   grounded on, hearsay, historical, implicit, inappealable,
   incontestable, incontrovertible, indicative, indubitable,
   irrefragable, irrefutable, irresistible, manifest, material,
   noticeable, nuncupative, observable, obvious, open-and-shut,
   out-and-out, outright, overwhelming, palpable, patent, perceivable,
   perceptible, peremptory, perfect, perspicuous, plain, plain as day,
   positive, presumptive, probative, provable, real, reliable, round,
   seeable, self-evident, self-explaining, self-explanatory,
   significant, straight, straight-out, suggestive, sure, symptomatic,
   tangible, telling, testable, to be seen, total, true, unanswerable,
   uncircumscribed, unconditional, unconditioned, unconfutable,
   uncontestable, undeniable, undoubting, unequivocal, unhampered,
   unhesitating, unimpeachable, unlimited, unmistakable, unmitigated,
   unqualified, unquestionable, unquestioning, unrefutable,
   unreserved, unrestricted, unwaivable, utter, valid, veridical,
   verifiable, visible, weighty, whole, without exception,
   without reserve