The term groin, sometimes spelled groyne—possibly from the Old French groyn, for the snout of a pig—is a construction either of wood or stone, or sometimes concrete, that extends out into the sea for the purpose of preventing the erosion of beaches, stopping the closing of channels from sedimentation, or to defend a pier or harbor from the action of the waves. Groins that project out into currents that run parallel to the shore work by disrupting the flow of the current and triggering the deposition of sand or other sediments. The word isn’t included in the 1828 Webster’s Dictionary, but it appears in a 1923 article by Philip P. Farley in the Municipal Engineers Journal: “Groynes of all types and sizes and more than thirty in number had been in existence along the Coney Island shore for many years.” It is in current use mostly on the Atlantic coast, where beach preservation has been an engineering issue. Cornelia Dean, in Against the Tide: The Battle for America’s Beaches, writes, “Groins, often incorrectly referred to as jetties, are short rock ribs that begin on the sand under the beach and run into the sea, sticking out like fingers into the surf to trap sand.” A group of groins is a groin field.

Robert Hass