The Collaborative International Dictionary of English v.0.48:

Jetty \Jet"ty\, a.
   Made of jet, or like jet in color.
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         The people . . . are of a jetty.         --Sir T.
                                                  Browne.
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The Collaborative International Dictionary of English v.0.48:

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.
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   2. A wharf or pier extending from the shore.
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   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.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Jetty \Jet"ty\, v. i.
   To jut out; to project. [Obs.] --Florio.
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WordNet (r) 3.0 (2006):

jetty
    n 1: a protective structure of stone or concrete; extends from
         shore into the water to prevent a beach from washing away
         [syn: breakwater, groin, groyne, mole, bulwark,
         seawall, jetty]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "jetty":
   abutment, anchorage, anchorage ground, arc-boutant, arch dam,
   backstop, bamboo curtain, bank, bar, barrage, barrier, basin, beam,
   bear-trap dam, beaver dam, berth, black, boom, breakwater,
   breastwork, brick wall, buffer, bulkhead, bulwark, buttress,
   buttress pier, buttressing, cofferdam, dam, defense, dike, ditch,
   dock, dockage, dockyard, dry dock, earthwork, ebon, ebony,
   embankment, fence, flying buttress, gate, gravity dam, groin,
   hanging buttress, harbor, harborage, haven, hydraulic-fill dam,
   inky, iron curtain, jam, jet, jutty, landing, landing place,
   landing stage, leaping weir, levee, logjam, marina, milldam, moat,
   mole, moorings, mound, parapet, pier, pier buttress, pitch-black,
   pitch-dark, port, portcullis, protected anchorage, quay, rampart,
   raven, retaining wall, road, roadblock, roads, roadstead,
   rock-fill dam, sable, seaport, seawall, shipyard, shoulder,
   shutter dam, slip, stone wall, wall, weir, wharf, wicket dam,
   work