breakwater

noun3

1. •
   A construction in or around a harbour designed to break the force of the sea and to provide shelter for vessels lying inside.

   • But there's a pier or breakwater runs out into the sea just here, which we could defend longer than anything else, like Horatius and his bridge. — 1908
2. •
   A low bulkhead across the forecastle deck of a ship which diverts water breaking over the bows into the scuppers.
3. •
   A wooden or concrete barrier, usually perpendicular to the shore, intended to prevent the movement of sand along a coast.