The Collaborative International Dictionary of English v.0.48:

Pier \Pier\, n. [OE. pere, OF. piere a stone, F. pierre, fr. L.
   petra, Gr. ?. Cf. Petrify.]
   1. (Arch.)
      (a) Any detached mass of masonry, whether insulated or
          supporting one side of an arch or lintel, as of a
          bridge; the piece of wall between two openings.
      (b) Any additional or auxiliary mass of masonry used to
          stiffen a wall. See Buttress.
          [1913 Webster]

   2. A projecting wharf or landing place.
      [1913 Webster]

   Abutment pier, the pier of a bridge next the shore; a pier
      which by its strength and stability resists the thrust of
      an arch.

   Pier glass, a mirror, of high and narrow shape, to be put
      up between windows.

   Pier table, a table made to stand between windows.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pier
    n 1: a platform built out from the shore into the water and
         supported by piles; provides access to ships and boats
         [syn: pier, wharf, wharfage, dock]
    2: (architecture) a vertical supporting structure (as a portion
       of wall between two doors or windows)
    3: a support for two adjacent bridge spans

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "pier":
   abutment, anchorage, anchorage ground, arc-boutant, arcade, atlas,
   baluster, balustrade, banister, bank, base, basin, beam, berth,
   breakwater, bulkhead, bulwark, buttress, buttress pier,
   buttressing, caryatid, colonnade, colonnette, column, dado, die,
   dock, dockage, dockyard, dry dock, embankment, flying buttress,
   footstalk, groin, hanging buttress, harbor, harborage, haven, jack,
   jetty, jutty, landing, landing place, landing stage, levee, marina,
   mole, moorings, newel-post, pedestal, pedicel, peduncle, peristyle,
   pier buttress, pilaster, pile, piling, pillar, plinth, pole, port,
   portico, post, protected anchorage, quay, queen-post, rampart,
   retaining wall, road, roads, roadstead, seaport, seawall, shaft,
   shipyard, shoulder, slip, socle, staff, stalk, stanchion, stand,
   standard, stem, subbase, support, surbase, telamon, trunk, upright,
   wharf, wharfage