The Collaborative International Dictionary of English v.0.48:

Ballet \Bal"let`\ (b[a^]l"l[asl]` or b[a^]l"l[e^]t; 277), n.
   [F., a dim. of bal dance. See 2d Ball, n.]
   1. An artistic dance performed as a theatrical entertainment,
      or an interlude, by a number of persons, usually women.
      Sometimes, a scene accompanied by pantomime and dancing.
      [1913 Webster]

   2. The company of persons who perform the ballet.
      [1913 Webster]

   3. (Mus.) A light part song, or madrigal, with a fa la burden
      or chorus, -- most common with the Elizabethan madrigal
      composers; -- also spelled ballett.
      [1913 Webster]

   4. (Her.) A bearing in coats of arms, representing one or
      more balls, which are denominated bezants, plates, etc.,
      according to color.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ballet
    n 1: a theatrical representation of a story that is performed to
         music by trained dancers [syn: ballet, concert dance]
    2: music written for a ballet