NOUN (2)

1. (Greek mythology) the son of Zeus who slew Medusa (with the help of Athena and Hermes) and rescued Andromeda from a sea monster;

2. a conspicuous constellation in the northern hemisphere; between Auriga and Cassiopeia and crossed by the Milky Way;

The Collaborative International Dictionary of English v.0.48:

Perseus \Per"se*us\, prop. n. [L., from Gr. Persey`s.]
   1. (Class. Myth.) A Grecian legendary hero, son of Jupiter
      and Dana["e], who slew the Gorgon Medusa.
      [1913 Webster]

   2. (Astron.) A consellation of the northern hemisphere, near
      Taurus and Cassiopea. It contains a star cluster visible
      to the naked eye as a nebula.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Perseus
    n 1: (Greek mythology) the son of Zeus who slew Medusa (with the
         help of Athena and Hermes) and rescued Andromeda from a sea
         monster
    2: a conspicuous constellation in the northern hemisphere;
       between Auriga and Cassiopeia and crossed by the Milky Way