The Collaborative International Dictionary of English v.0.48:

Athanasian \Ath`a*na"sian\ (?; 277), a.
   Of or pertaining to Athanasius, bishop of Alexandria in the
   4th century.
   [1913 Webster]

   Athanasian creed, a formulary, confession, or exposition of
      faith, formerly supposed to have been drawn up by
      Athanasius; but this opinion is now rejected, and the
      composition is ascribed by some to Hilary, bishop of Arles
      (5th century). It is a summary of what was called the
      orthodox faith.
      [1913 Webster]