"strong, low sea wall," 1580s, perhaps from obsolete groin "pig's snout" (c. 1300; the wall so called because it was thought to look like one), from Old French groin "muz [..]

a wooden wall built across a beach from land to sea. Designed in the 19th century to stop the removal of sand from beaches becoming popular with new tourists, they became important parts of many coast [..]

(n) a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away

A low wall-like structure, generally of wood or stone, usually extending at right angles from the shore, to prevent erosion. Frequently erected in estuaries and rivers to direct the flow of the water [..]

wooden breakwater.

A breakwater running seawards from the land, constructed to stop the flow of beach material transported by longshore drift.