The Collaborative International Dictionary of English v.0.48:

Unchallenged \Unchallenged\
   See challenged.

WordNet (r) 3.0 (2006):

unchallenged
    adj 1: generally agreed upon; not subject to dispute; "the
           undisputed fact" [syn: undisputed, unchallenged,
           unquestioned]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "unchallenged":
   agreeing, at one, at one with, beyond question,
   carried by acclamation, concordant, concurrent, consentaneous,
   doubtless, in agreement, indubious, like-minded, of a piece,
   of one accord, of one mind, past dispute, questionless, solid,
   unanimous, uncontested, uncontradicted, uncontroversial,
   uncontroverted, undisputed, undoubted, unopposed, unquestioned,
   with one consent, with one voice