Source : Webster's Revised Unabridged Dictionary (1913)

Breakwater \Break"wa`ter\, n.
   Any structure or contrivance, as a mole, or a wall at the
   mouth of a harbor, to break the force of waves, and afford
   protection from their violence.

Source : WordNet®

breakwater
     n : a protective structure of stone or concrete; extends from
         shore into the water to prevent a beach from washing away
         [syn: {groin}, {groyne}, {mole}, {bulwark}, {seawall}, {jetty}]