The Collaborative International Dictionary of English v.0.48:

Manes \Ma"nes\, n. pl. [L.] (Rom. Antiq.)
   The benevolent spirits of the dead, especially of dead
   ancestors, regarded as family deities and protectors.
   [1913 Webster]

         Hail, O ye holy manes!                   --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Manes
    n 1: a Persian prophet who founded Manichaeism (216-276)

The Devil's Dictionary (1881-1906):

MANES, n.  The immortal parts of dead Greeks and Romans.  They were in
a state of dull discomfort until the bodies from which they had
exhaled were buried and burned; and they seem not to have been
particularly happy afterward.