The Collaborative International Dictionary of English v.0.48:

Ledge \Ledge\ (l[e^]j), n. [Akin to AS. licgan to lie, Icel.
   liggja; cf. Icel. l["o]gg the ledge or rim at the bottom of a
   cask. See Lie to be prostrate.] [Formerly written lidge.]
   1. A shelf on which articles may be laid; also, that which
      resembles such a shelf in form or use, as a projecting
      ridge or part, or a molding or edge in joinery.
      [1913 Webster]

   2. A shelf, ridge, or reef, of rocks.
      [1913 Webster]

   3. A layer or stratum.
      [1913 Webster]

            The lowest ledge or row should be of stone. --Sir H.
                                                  Wotton.
      [1913 Webster]

   4. (Mining) A lode; a limited mass of rock bearing valuable
      mineral.
      [1913 Webster]

   5. (Shipbuilding) A piece of timber to support the deck,
      placed athwartship between beams.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ledge
    n 1: a projecting ridge on a mountain or submerged under water
         [syn: ledge, shelf]

Moby Thesaurus II by Grady Ward, 1.0:

121 Moby Thesaurus words for "ledge":
   band, bank, beam-end, bed, bedding, belt, billiard table, board,
   border, bordure, bowling green, brim, brink, brow, coast,
   coral heads, corbel, couche, course, dead flat, dead level, deck,
   earth, edge, esplanade, featheredge, flange, flat, flatland, floor,
   frame, fringe, gallery, gradin, gradino, ground, hem, hob,
   homaloid, horizontal, horizontal axis, horizontal fault,
   horizontal line, horizontal parallax, horizontal plane,
   horizontal projection, ironbound coast, labellum, labium, labrum,
   layer, ledges, lee shore, level, level line, level plane, limb,
   limbus, lip, list, mantel, mantelshelf, mantle, marge, margin,
   mean sea level, measures, overhang, overlayer, overstory, parterre,
   pitfall, plain, plane, platform, prairie, predella, projection,
   quicksands, ragged edge, retable, rim, rockbound coast, rocks,
   sandbank, sandbar, sands, sea level, sea of grass, seam, selvage,
   shallows, shelf, shoals, shore, shoulder, side, sideline, sill,
   skirt, stage, step, steppe, story, stratum, substratum, superaltar,
   superstratum, table, terrace, thickness, tier, topsoil,
   undercurrent, underlayer, understory, understratum, undertow,
   verge, water level, zone