NOUN (2)

1. (Greek mythology) 7 daughters of Atlas and half-sisters of the Hyades; placed among the stars to save them from the pursuit of Orion;

2. a star cluster in the constellation Taurus;

The Collaborative International Dictionary of English v.0.48:

Pleiades \Ple"ia*des\ (?; 277), n. pl. [L., fr. Gr. (?)]
   1. (Myth.) The seven daughters of Atlas and the nymph
      Pleione, fabled to have been made by Jupiter a
      constellation in the sky.
      [1913 Webster]

   2. (Astron.) A group of small stars in the neck of the
      constellation Taurus; -- called also the seven sisters.
      --Job xxxviii. 31.
      [1913 Webster]

   Note: Alcyone, the brightest of these, a star of the third
         magnitude, was considered by M[aum]dler the central
         point around which our universe is revolving, but such
         a notion has been thoroughly discounted by modern
         observations. Only six pleiads are distinctly visible
         to the naked eye, whence the ancients supposed that a
         sister had concealed herself out of shame for having
         loved a mortal, Sisyphus.
         [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

Pleiades
    n 1: (Greek mythology) 7 daughters of Atlas and half-sisters of
         the Hyades; placed among the stars to save them from the
         pursuit of Orion
    2: a star cluster in the constellation Taurus