Source : Webster's Revised Unabridged Dictionary (1913)

Sponson \Spon"son\, n. (Shipbuilding)
   (a) One of the triangular platforms in front of, and abaft,
       the paddle boxes of a steamboat.
   (b) One of the slanting supports under the guards of a
       steamboat.
   (c) One of the armored projections fitted with gun ports,
       used on modern war vessels.