The Collaborative International Dictionary of English v.0.48:

Gallery \Gal"ler*y\, n.; pl. Galleries. [F. galerie, It.
   galleria, fr. LL. galeria gallery, perh. orig., a festal
   hall, banquetting hall; cf. OF. galerie a rejoicing, fr.
   galer to rejoice. Cf. Gallant, a.]
   1. A long and narrow corridor, or place for walking; a
      connecting passageway, as between one room and another;
      also, a long hole or passage excavated by a boring or
      burrowing animal.
      [1913 Webster]

   2. A room for the exhibition of works of art; as, a picture
      gallery; hence, also, a large or important collection of
      paintings, sculptures, etc.
      [1913 Webster]

   3. A long and narrow platform attached to one or more sides
      of public hall or the interior of a church, and supported
      by brackets or columns; -- sometimes intended to be
      occupied by musicians or spectators, sometimes designed
      merely to increase the capacity of the hall.
      [1913 Webster]

   4. (Naut.) A frame, like a balcony, projecting from the stern
      or quarter of a ship, and hence called stern gallery or
      quarter gallery, -- seldom found in vessels built since
      1850.
      [1913 Webster]

   5. (Fort.) Any communication which is covered overhead as
      well as at the sides. When prepared for defense, it is a
      defensive gallery.
      [1913 Webster]

   6. (Mining) A working drift or level.
      [1913 Webster]

   Whispering gallery. See under Whispering.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gallery
    n 1: spectators at a golf or tennis match
    2: a porch along the outside of a building (sometimes partly
       enclosed) [syn: veranda, verandah, gallery]
    3: a room or series of rooms where works of art are exhibited
       [syn: gallery, art gallery, picture gallery]
    4: a long usually narrow room used for some specific purpose;
       "shooting gallery"
    5: a covered corridor (especially one extending along the wall
       of a building and supported with arches or columns)
    6: narrow recessed balcony area along an upper floor on the
       interior of a building; usually marked by a colonnade
    7: a horizontal (or nearly horizontal) passageway in a mine;
       "they dug a drift parallel with the vein" [syn: drift,
       heading, gallery]

Moby Thesaurus II by Grady Ward, 1.0:

208 Moby Thesaurus words for "gallery":
   British Museum, Guggenheim Museum, Hermitage, Louvre,
   Metropolitan Museum, National Gallery, Prado, Rijksmuseum,
   Tate Gallery, Texas tower, Uffizi, abri, access, aisle, alley,
   ambulatory, amphitheater, aperture, approach trench, arcade,
   areaway, arena, art gallery, artery, assembly hall, atelier,
   audience, auditorium, auditory, avenue, balcony, band, beacon, bed,
   bedding, belt, belvedere, bleachers, box, box seat, breezeway,
   bridge, bunker, catafalque, channel, chapel, cloister, colonnade,
   communication, communication trench, concert hall, conduit,
   congregation, connection, conning tower, convention hall, corridor,
   couche, countermine, coupure, course, covered way, curatorship,
   dais, dance hall, deck, defile, display room, ditch, double sap,
   dress circle, dugout, emplacement, entrenchment, estrade,
   exhibition hall, exhibition room, exit, fauteuil, ferry,
   fire trench, floor, flying sap, ford, fortified tunnel, fosse,
   foxhole, gazebo, grandstand, groundling, hall, hallway, heliport,
   house, hustings, inlet, interchange, intersection, junction, lanai,
   landing, landing pad, landing stage, lane, launching pad, layer,
   lecture hall, ledge, level, lighthouse, loge, loggia, lookout,
   loophole, measures, meetinghouse, mine, moat, museology, museum,
   music hall, nigger heaven, observation post, observatory, opening,
   opera house, orchestra, orchestra circle, outlet, outlook,
   overlayer, overlook, overpass, overstory, paradise, parallel,
   parquet, parquet circle, parterre, pass, passage, passageway,
   patio, peanut gallery, peephole, pergola, peristyle, pharos,
   piazza, picture gallery, pinacotheca, pit, platform, podium, porch,
   portico, proscenium boxes, pulpit, railroad tunnel, ringside,
   ringside seat, rostrum, salon, sap, seam, shelf, showroom,
   sighthole, sleeping porch, slit trench, soapbox, solarium,
   spectator, stadium, stage, stall, standing room, step,
   step terrace, stoop, story, stratum, studio, stump, substratum,
   sun porch, superstratum, terrace, theater, theatre stall,
   thickness, tier, top gallery, topsoil, tower, traject, trajet,
   trench, tribunal, tribune, tunnel, underlayer, underpass,
   understory, understratum, veranda, watchtower, zone



Easton's 1897 Bible Dictionary:

Gallery
   (1.) Heb. 'attik (Ezek. 41:15, 16), a terrace; a projection;
   ledge.

     (2.) Heb. rahit (Cant. 1:17), translated "rafters," marg.
   "galleries;" probably panel-work or fretted ceiling.