Jetty \Jet"ty\, n.; pl. {Jetties}. [F. jet['e]e a pier, a jetty, a causeway. See {Jet} a shooting forth, and cf. {Jutty}.] [1913 Webster] 1. (Arch.) A part of a building that jets or projects beyond the rest, and overhangs the wall below. [1913 Webster] 2. A wharf or pier extending from the shore. [1913 Webster] 3. (Hydraul. Engin.) A structure of wood or stone extended into the sea to influence the current or tide, or to protect a harbor; a mole; as, the Eads system of jetties at the mouth of the Mississippi River. [1913 Webster] {Jetty head} (Naut.), a projecting part at the end of a wharf; the front of a wharf whose side forms one of the cheeks of a dock. [1913 Webster]