Source : Webster's Revised Unabridged Dictionary (1913)

Doorstep \Door"step`\, n.
   The stone or plank forming a step before an outer door.

Source : WordNet®

doorstep
     n : the sill of a door; a horizontal piece of wood or stone that
         forms the bottom of a doorway and offer support when
         passing through a doorway [syn: {doorsill}, {threshold}]