undeniably

from WordNet (r) 3.0 (2006)

undeniably
    adv 1: to an undeniable degree or in an undeniable manner; "she
           is undeniably the most gifted student in the class"

from The Collaborative International Dictionary of English v.0.48

Undeniably \Un`de*ni"a*bly\, adv.
   In an undeniable manner.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

40 Moby Thesaurus words for "undeniably":
      actually, admittedly, assuredly, beyond doubt, beyond question,
      certainly, clearly, decidedly, demonstrably, doubtless,
      doubtlessly, for a certainty, for real, in all conscience,
      incontestably, indeed, indisputably, indubitably, irrefragably,
      irrefutably, manifestly, no doubt, noticeably, observably,
      obviously, out of question, patently, positively, quite, really,
      sensibly, seriously, truly, unambiguously, undoubtedly,
      unmistakably, unquestionably, verily, visibly, without doubt