The Collaborative International Dictionary of English v.0.48:

Pyrrhic \Pyr"rhic\, n.
   1. [Gr. ?: cf. F. pyrrhique, fem.] An ancient Greek martial
      dance, to the accompaniment of the flute, its time being
      very quick.
      [1913 Webster]

   2. [L. pyrrhichius (sc. pes), Gr. ? (sc. ?): cf. F.
      pyrrhique, masc.] (Pros.) A foot consisting of two short
      syllables.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pyrrhic \Pyr"rhic\, a. [L. pyrrhichius, Gr. ? belonging to the ?
   (sc. ?) a kind of war dance.]
   1. Of or pertaining to an ancient Greek martial dance. " ye
      have the pyrrhic dance as yet." --Byron.
      [1913 Webster]

   2. (Pros.) Of or pertaining to a pyrrhic, or to pyrrhics;
      containing pyrrhic; as, a pyrrhic verse.
      [1913 Webster]

   Pyrrhic victory [From Pyrrhus, king of Epirus.],
      (a) a victory in which the winning side sustains very
          heavy losses.
      (b) any act supposedly benefitting the actor, for which
          the costs outweight the benefits.
          [PJC]

WordNet (r) 3.0 (2006):

pyrrhic
    adj 1: of or relating to a war dance of ancient Greece; "pyrrhic
           dance movements"
    2: of or relating to or containing a metrical foot of two
       unstressed syllables; "pyrrhic verses"
    3: of or relating to or resembling Pyrrhus or his exploits
       (especially his sustaining staggering losses in order to
       defeat the Romans); "a Pyrrhic victory"
    n 1: a metrical unit with unstressed-unstressed syllables [syn:
         pyrrhic, dibrach]
    2: an ancient Greek dance imitating the motions of warfare