The Collaborative International Dictionary of English v.0.48:

Wildfire \Wild"fire\, n.
   1. A composition of inflammable materials, which, kindled, is
      very hard to quench; Greek fire.
      [1913 Webster]

            Brimstone, pitch, wildfire . . . burn cruelly, and
            hard to quench.                       --Bacon.
      [1913 Webster]

   2. (Med.)
      (a) An old name for erysipelas.
      (b) A disease of sheep, attended with inflammation of the
          skin.
          [1913 Webster]

   3. A sort of lightning unaccompanied by thunder. [R.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

wildfire
    n 1: a raging and rapidly spreading conflagration