The Collaborative International Dictionary of English v.0.48:

Serapis \Se*ra"pis\, n. [L., fr. Gr. ???, ???.] (Myth.)
   An Egyptian deity, at first a symbol of the Nile, and so of
   fertility; later, one of the divinities of the lower world.
   His worship was introduced into Greece and Rome.
   [1913 Webster]