NOUN (4)

1. a shelter or screen providing protection from enemy fire or from the weather;

2. a small fort or earthwork defending a ford, pass, or castle gate;

3. a candle or flaming torch secured in a sconce;

4. a decorative wall bracket for holding candles or other sources of light;

The Collaborative International Dictionary of English v.0.48:

Sconce \Sconce\, n. [D. schans, OD. schantse, perhaps from OF.
   esconse a hiding place, akin to esconser to hide, L.
   absconsus, p. p. of abscondere. See Abscond, and cf.
   Ensconce, Sconce a candlestick.]
   1. A fortification, or work for defense; a fort.
      [1913 Webster]

            No sconce or fortress of his raising was ever known
            either to have been forced, or yielded up, or
            quitted.                              --Milton.
      [1913 Webster]

   2. A hut for protection and shelter; a stall.
      [1913 Webster]

            One that . . . must raise a sconce by the highway
            and sell switches.                    --Beau. & Fl.
      [1913 Webster]

   3. A piece of armor for the head; headpiece; helmet.
      [1913 Webster]

            I must get a sconce for my head.      --Shak.
      [1913 Webster]

   4. Fig.: The head; the skull; also, brains; sense;
      discretion. [Colloq.]
      [1913 Webster]

            To knock him about the sconce with a dirty shovel.
                                                  --Shak.
      [1913 Webster]

   5. A poll tax; a mulct or fine. --Johnson.
      [1913 Webster]

   6. [OF. esconse a dark lantern, properly, a hiding place. See
      Etymol. above.] A protection for a light; a lantern or
      cased support for a candle; hence, a fixed hanging or
      projecting candlestick.
      [1913 Webster]

            Tapers put into lanterns or sconces of
            several-colored, oiled paper, that the wind might
            not annoy them.                       --Evelyn.
      [1913 Webster]

            Golden sconces hang not on the walls. --Dryden.
      [1913 Webster]

   7. Hence, the circular tube, with a brim, in a candlestick,
      into which the candle is inserted.
      [1913 Webster]

   8. (Arch.) A squinch.
      [1913 Webster]

   9. A fragment of a floe of ice. --Kane.
      [1913 Webster]

   10. [Perhaps a different word.] A fixed seat or shelf. [Prov.
       Eng.]
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sconce \Sconce\, v. t. [imp. & p. p. Sconced; p. pr. & vb. n.
   Sconcing.]
   1. To shut up in a sconce; to imprison; to insconce. [Obs.]
      [1913 Webster]

            Immure him, sconce him, barricade him in 't.
                                                  --Marston.
      [1913 Webster]

   2. To mulct; to fine. [Obs.] --Milton.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Squinch \Squinch\ (skw[i^]nch), n. [Corrupted fr. sconce.]
   (Arch.)
   A small arch thrown across the corner of a square room to
   support a superimposed mass, as where an octagonal spire or
   drum rests upon a square tower; -- called also sconce, and
   sconcheon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sconce
    n 1: a shelter or screen providing protection from enemy fire or
         from the weather
    2: a small fort or earthwork defending a ford, pass, or castle
       gate
    3: a candle or flaming torch secured in a sconce
    4: a decorative wall bracket for holding candles or other
       sources of light

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "sconce":
   abatis, advanced work, amercement, balistraria, bank, banquette,
   barbed-wire entanglement, barbican, barricade, barrier, bartizan,
   bastion, battlement, bean, belfry, bracket, brain, breastwork,
   brow, bulwark, candelabrum, candlestand, candlestick, casemate,
   chandelier, cheval-de-frise, chump, circumvallation, conk,
   contravallation, counterscarp, crown, curtain, damages,
   demibastion, dike, distraint, distress, dome, drawbridge,
   earthwork, encephalon, enclosure, entanglement, escarp, escarpment,
   escheat, escheatment, fence, fieldwork, fine, forfeit, forfeiture,
   fortalice, fortification, gas fixture, girandole, glacis,
   gray matter, head, headpiece, lamp holder, lampstand,
   light fixture, light socket, loophole, lunette, machicolation,
   mantelet, merlon, mound, mulct, noddle, noggin, noodle,
   organ of thought, outwork, palisade, parados, parapet, pate, poll,
   portcullis, postern gate, rampart, ravelin, redan, redoubt, ridge,
   sally port, scarp, seat of thought, sensation, sensorium, sensory,
   stockade, tenaille, torch holder, torch staff, vallation, vallum,
   wall bracket, work