breakwater(n = noun.artifact) bulwark, groin, groyne, jetty, mole, seawall - a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away;
is a kind of barrier

   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. [1913 Webster]

breakwater, n. a barrier built out into the sea to break the force of waves.

N  refuge, sanctuary, retreat, fastness, acropolis, keep, last resort, ward, prison, asylum, ark, home, refuge for the destitute, almshouse, hiding place, sanctum sanctorum, roadstead, anchorage, breakwater, mole, port, haven, harbor, harbor of refuge, seaport, pier, jetty, embankment, quay, covert, cover, shelter, screen, lee wall, wing, shield, umbrella, barrier, dashboard, dasher, wall, fort, anchor, kedge, grapnel, grappling iron, sheet anchor, killick, mainstay, support, cheek, ballast, jury mast, vent-peg, safety valve, blow-off valve, safety lamp, lightning rod, lightning conductor, safety belt, airbag, seat belt, antilock brakes, antiskid tires, snow tires, means of escape, lifeboat, lifejacket, life buoy, swimming belt, cork jacket, parachute, plank, steppingstone, emergency landing, safeguard, any port in a storm, bibere venenum in auro, valet anchora virtus.