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.
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            No sconce or fortress of his raising was ever known
            either to have been forced, or yielded up, or
            quitted.                              --Milton.
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   2. A hut for protection and shelter; a stall.
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            One that . . . must raise a sconce by the highway
            and sell switches.                    --Beau. & Fl.
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   3. A piece of armor for the head; headpiece; helmet.
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            I must get a sconce for my head.      --Shak.
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   4. Fig.: The head; the skull; also, brains; sense;
      discretion. [Colloq.]
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            To knock him about the sconce with a dirty shovel.
                                                  --Shak.
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   5. A poll tax; a mulct or fine. --Johnson.
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   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.
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            Tapers put into lanterns or sconces of
            several-colored, oiled paper, that the wind might
            not annoy them.                       --Evelyn.
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            Golden sconces hang not on the walls. --Dryden.
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   7. Hence, the circular tube, with a brim, in a candlestick,
      into which the candle is inserted.
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   8. (Arch.) A squinch.
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   9. A fragment of a floe of ice. --Kane.
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   10. [Perhaps a different word.] A fixed seat or shelf. [Prov.
       Eng.]
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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.]
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            Immure him, sconce him, barricade him in 't.
                                                  --Marston.
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   2. To mulct; to fine. [Obs.] --Milton.
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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.
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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