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.
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            The king serves only as a notary to authenticate the
            choice of judges.                     --Burke.
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   2. To prove authentic; to determine as real and true; as, to
      authenticate a portrait. --Walpole.
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