Source : Webster's Revised Unabridged Dictionary (1913)

Riser \Ris"er\, n.
   1. One who rises; as, an early riser.

   2. (Arch.)
      (a) The upright piece of a step, from tread to tread.
          Hence:
      (b) Any small upright face, as of a seat, platform,
          veranda, or the like.

   3. (Mining) A shaft excavated from below upward.

   4. (Founding) A feed head. See under {Feed}, n.

Source : WordNet®

riser
     n 1: a person who rises (especially from bed); "he's usually a
          late riser"
     2: a vertical pipe in a building [syn: {riser pipe}, {riser
        pipeline}, {riser main}]
     3: structural member consisting of the vertical part of a stair
        or step