The Collaborative International Dictionary of English v.0.48:

Cassiopeia \Cas`si*o*pe"ia\, n. [NL., fr. Gr. ?.] (Astron.)
   A constellation of the northern hemisphere, situated between
   Cepheus and Perseus; -- so called in honor of the wife of
   Cepheus, a fabulous king of Ethiopia.
   [1913 Webster]

   Cassiopeia's Chair, a group of six stars, in Cassiopeia,
      somewhat resembling a chair.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Cassiopeia
    n 1: (Greek mythology) the wife of Cepheus and mother of
         Andromeda
    2: a W-shaped constellation in the northern hemisphere near
       Polaris