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 victory
    n 1: a victory that is won by incurring terrible losses

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "Pyrrhic victory":
   Cadmean victory, KO, ascendancy, championship, conquest,
   easy victory, grand slam, knockout, landslide, landslide victory,
   mastery, moral victory, picnic, pushover, runaway victory, subdual,
   subduing, success, total victory, triumph, victory, walkaway,
   walkover, win, winning, winning streak