Source : Webster's Revised Unabridged Dictionary (1913)

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

            Brimstone, pitch, wildfire . . . burn cruelly, and
            hard to quench.                       --Bacon.

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

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

Source : WordNet®

wildfire
     n : a raging and rapidly spreading conflagration