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]

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]

The Free On-line Dictionary of Computing (19 January 2023):

irrefutable

   The opposite of refutable.