The Collaborative International Dictionary of English v.0.48:

Gettysburg \Gettysburg\ prop. n.
   The name of a battle of the American Civil War fought in and
   around the town of Gettysburg, Pennsylavania, in 1863. At
   this battle, the defeat of General Robert E. Lee's invading
   Confederate army was a major victory for the Union, and is
   considered by many a turning point in the war, after which
   victory by the Confederacy was no longer thought possible;
   as, many thousands died at Gettysburg. See also Gettysburg
   Address.

   Syn: battle of Gettysburg.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

Gettysburg
    n 1: a small town in southern Pennsylvania; site of a national
         cemetery
    2: a battle of the American Civil War (1863); the defeat of
       Robert E. Lee's invading Confederate Army was a major victory
       for the Union [syn: Gettysburg, Battle of Gettysburg]