The Collaborative International Dictionary of English v.0.48:

Embankment \Em*bank"ment\, n.
   1. The act of surrounding or defending with a bank.
      [1913 Webster]

   2. A structure of earth, gravel, etc., raised to prevent
      water from overflowing a level tract of country, to retain
      water in a reservoir, or to carry a roadway, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

embankment
    n 1: a long artificial mound of stone or earth; built to hold
         back water or to support a road or as protection

Moby Thesaurus II by Grady Ward, 1.0:

180 Moby Thesaurus words for "embankment":
   L, abutment, anchorage, anchorage ground, anthill, arc-boutant,
   arch dam, backstop, bamboo curtain, bank, bar, barrage, barrier,
   basin, beach, beam, bear-trap dam, beaver dam, berm, berth, boom,
   branch, breakwater, breastwork, brick wall, buffer, bulkhead,
   bulwark, buttress, buttress pier, buttressing, cable railway,
   coast, coastland, coastline, cock, cofferdam, cog railway, dam,
   defense, dike, ditch, dock, dockage, dockyard, drift, dry dock,
   dune, earthwork, el, electric railway, elevated, elevated railway,
   feeder, feeder line, fence, flying buttress, foreshore, gate,
   gravity dam, gravity-operated railway, groin, hanging buttress,
   harbor, harborage, haven, haycock, haymow, hayrick, haystack, heap,
   hill, horse railway, hydraulic-fill dam, iron curtain,
   ironbound coast, jam, jetty, junction, jutty, landing,
   landing place, landing stage, leaping weir, levee, lido,
   light railroad, line, littoral, logjam, main line, marina, metro,
   milldam, moat, mole, molehill, monorail, moorings, mound, mow,
   parapet, pier, pier buttress, pile, plage, playa, port, portcullis,
   protected anchorage, pyramid, quay, rack railway,
   rack-and-pinion railway, rail, rail line, railroad, railway,
   rampart, retaining wall, rick, riverside, riviera, road, roadbed,
   roadblock, roads, roadstead, roadway, rock-fill dam,
   rockbound coast, sands, sea margin, seabank, seabeach, seaboard,
   seacliff, seacoast, seaport, seashore, seaside, seawall, shingle,
   shipyard, shore, shoreline, shoulder, shutter dam, sidetrack,
   siding, slip, snowdrift, stack, stone wall, strand, street railway,
   streetcar line, submerged coast, subway, switchback, terminal,
   terminus, tidewater, track, tram, tramline, trestle, trolley line,
   trunk, trunk line, tube, turnout, underground, wall, waterfront,
   waterside, weir, wharf, wicket dam, work