The Collaborative International Dictionary of English v.0.48:

Gallows \Gal"lows\, n. sing.; pl. Gallowsesor Gallows. [OE.
   galwes, pl., AS. galga, gealga, gallows, cross; akin to D.
   galg gallows, OS. & OHG. galgo, G. galgen, Icel. g[=a]lgi,
   Sw. & Dan. galge, Goth. galga a cross. Etymologically and
   historically considered, gallows is a noun in the plural
   number, but it is used as a singular, and hence is preceded
   by a; as, a gallows.]
   1. A frame from which is suspended the rope with which
      criminals are executed by hanging, usually consisting of
      two upright posts and a crossbeam on the top; also, a like
      frame for suspending anything.
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            So they hanged Haman on the gallows.  --Esther vii.
                                                  10.
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            If I hang, I'll make a fat pair of gallows. --Shak.
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            O, there were desolation of gaolers and gallowses!
                                                  --Shak.
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   2. A wretch who deserves the gallows. [R.] --Shak.
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   3. (Print.) The rest for the tympan when raised.
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   4. pl. A pair of suspenders or braces. [Colloq.]
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   Gallows bird, a person who deserves the gallows. [Colloq.]


   Gallows bitts (Naut.), one of two or more frames amidships
      on deck for supporting spare spars; -- called also
      gallows, gallows top, gallows frame, etc.

   Gallows frame.
      (a) The frame supporting the beam of an engine.
      (b) (Naut.) Gallows bitts.

   Gallows tree, or

   Gallow tree, the gallows.
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            At length him nail['e]d on a gallow tree. --Spenser.
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WordNet (r) 3.0 (2006):

gallows
    n 1: an instrument of execution consisting of a wooden frame
         from which a condemned person is executed by hanging

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "gallows":
   ax, beheading, block, burning, capital punishment, cross,
   crucifixion, death chair, death chamber, decapitation, decollation,
   defenestration, drop, electric chair, electrocution, execution,
   fusillade, gallows-tree, garrote, gas chamber, gassing, gibbet,
   guillotine, halter, hanging, hemlock, hemp, hempen collar,
   hot seat, judicial murder, lapidation, lethal chamber, maiden,
   necktie party, noose, poisoning, rope, scaffold, shooting, stake,
   stoning, strangling, strangulation, the ax, the block, the chair,
   the gallows, the gas chamber, the guillotine, the hot seat,
   the rope, tree



Easton's 1897 Bible Dictionary:

Gallows
   Heb. 'ets, meaning "a tree" (Esther 6:4), a post or gibbet. In
   Gen. 40:19 and Deut. 21:22 the word is rendered "tree."


Bouvier's Law Dictionary, Revised 6th Ed (1856):

GALLOWS. An erection on which to bang criminals condemned to death.



The Devil's Dictionary (1881-1906):

GALLOWS, n.  A stage for the performance of miracle plays, in which
the leading actor is translated to heaven.  In this country the
gallows is chiefly remarkable for the number of persons who escape it.

    Whether on the gallows high
        Or where blood flows the reddest,
    The noblest place for man to die --
        Is where he died the deadest.
                                                            (Old play)