The Collaborative International Dictionary of English v.0.48:

authenticated \authenticated\ adj.
   1. established or certified as genuine.

   Syn: attested, documented.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Authenticate \Au*then"ti*cate\, v. t. [imp. & p. p.
   Authenticated; p. pr. & vb. n. Authenticating (?).] [Cf.
   LL. authenticare.]
   1. To render authentic; to give authority to, by the proof,
      attestation, or formalities required by law, or sufficient
      to entitle to credit.
      [1913 Webster]

            The king serves only as a notary to authenticate the
            choice of judges.                     --Burke.
      [1913 Webster]

   2. To prove authentic; to determine as real and true; as, to
      authenticate a portrait. --Walpole.
      [1913 Webster]

WordNet (r) 3.0 (2006):

authenticated
    adj 1: established as genuine [syn: attested, authenticated,
           documented]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "authenticated":
   accepted, acknowledged, actual, admitted, affirmed, allowed,
   approved, ascertained, attested, avowed, borne out,
   categorically true, certain, certified, circumstantiated, conceded,
   confessed, confirmed, corroborated, countersigned, demonstrated,
   determined, documentary, effectual, endorsed, established, factual,
   fixed, granted, historical, not in error, notarized,
   objectively true, professed, proved, proven, ratified, real,
   received, recognized, sealed, settled, shown, signed, stamped,
   substantiated, sure-enough, sworn and affirmed, sworn to, true,
   true as gospel, truthful, unconfuted, undenied, underwritten,
   undoubted, unerroneous, unfallacious, unfalse, unmistaken,
   unquestionable, unrefuted, validated, veracious, verified,
   veritable, warranted