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

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]