The Collaborative International Dictionary of English v.0.48:

Panathenaea \Pan*ath`e*nae"a\, n. pl. [NL., fr. Gr. ?; pa^s
   pa^n, all + ? Athena.]
   The most ancient and important festival of Athens, celebrated
   in honor of Athena, the tutelary goddess of the city.
   [Webster 1913 Suppl.]