breakwater

noun

1. a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away

   noun.artifact

   Synonyms bulwark groin groyne jetty mole seawall

   Source: WordNet 3.0

2. 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.

   noun

   Source: webster1913