The Collaborative International Dictionary of English v.0.48:

Credential \Cre*den"tial\ (kr[-e]*d[e^]n"shal), a. [Cf. It.
   credenziale, fr. LL. credentia. See Credence.]
   Giving a title or claim to credit or confidence; accrediting.
   [1913 Webster]

         Their credential letters on both sides.  --Camden.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Credential \Cre*den"tial\, n. [Cf. It. credenziale.]
   1. That which gives a title to credit or confidence.
      [1913 Webster]

   2. pl. Testimonials showing that a person is entitled to
      credit, or has right to exercise official power, as the
      letters given by a government to an ambassador or envoy,
      or a certificate that one is a duly elected delegate.
      [1913 Webster]

            The committee of estates excepted against the
            credentials of the English commissioners.
                                                  --Whitelocke.
      [1913 Webster]

            Had they not shown undoubted credentials from the
            Divine Person who sent them on such a message.
                                                  --Addison.

WordNet (r) 3.0 (2006):

credential
    n 1: a document attesting to the truth of certain stated facts
         [syn: certificate, certification, credential,
         credentials]