Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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

Source : Free On-Line Dictionary of Computing

irrefutable
     
        The opposite of {refutable}.