irrefutable

from WordNet (r) 3.0 (2006)

irrefutable
    adj 1: impossible to deny or disprove; "incontrovertible proof
           of the defendant's innocence"; "proof positive"; "an
           irrefutable argument" [syn: {incontrovertible},
           {irrefutable}, {positive}]

from The Collaborative International Dictionary of English v.0.48

Irrefutable \Ir`re*fut"a*ble\ (?; 277), a. [L. irrefutabilis:
   cf. F. irr['e]futable. See {Refute}.]
   Incapable of being refuted or disproved; indisputable. --
   {Ir`re*fut"a*ble*ness}, n. -- {Ir`re*fut"a*bly}, adv.
   [1913 Webster]

from The Free On-line Dictionary of Computing (8 July 2008)

irrefutable

   The opposite of {refutable}.

from Moby Thesaurus II by Grady Ward, 1.0

67 Moby Thesaurus words for "irrefutable":
      absolute, actual, adducible, admissible, admitting no question,
      attestative, attestive, authentic, based on, certain,
      circumstantial, conclusive, confirmable, convincing, cumulative,
      damning, decisive, demonstrable, demonstratable, determinative,
      documentary, documented, evidential, evidentiary, ex parte,
      eye-witness, factual, final, firsthand, founded on, grounded on,
      hearsay, historical, implicit, inappealable, incontestable,
      incontrovertible, indicative, indisputable, indubitable,
      irrefragable, irresistible, material, nuncupative, overwhelming,
      presumptive, probative, provable, real, reliable, self-evident,
      significant, suggestive, sure, symptomatic, telling, testable,
      unanswerable, unconfutable, uncontestable, undeniable,
      unimpeachable, unquestionable, unrefutable, valid, verifiable,
      weighty