The Collaborative International Dictionary of English v.0.48:

Labor \La"bor\ (l[=a]"b[~e]r), n. [OE. labour, OF. labour,
   laber, labur, F. labeur, L. labor; cf. Gr. lamba`nein to
   take, Skr. labh to get, seize.] [Written also labour.]
   1. Physical toil or bodily exertion, especially when
      fatiguing, irksome, or unavoidable, in distinction from
      sportive exercise; hard, muscular effort directed to some
      useful end, as agriculture, manufactures, and like;
      servile toil; exertion; work.
      [1913 Webster]

            God hath set
            Labor and rest, as day and night, to men
            Successive.                           --Milton.
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   2. Intellectual exertion; mental effort; as, the labor of
      compiling a history.
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   3. That which requires hard work for its accomplishment; that
      which demands effort.
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            Being a labor of so great a difficulty, the exact
            performance thereof we may rather wish than look
            for.                                  --Hooker.
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   4. Travail; the pangs and efforts of childbirth.
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            The queen's in labor,
            They say, in great extremity; and feared
            She'll with the labor end.            --Shak.
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   5. Any pang or distress. --Shak.
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   6. (Naut.) The pitching or tossing of a vessel which results
      in the straining of timbers and rigging.
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   7. [Sp.] A measure of land in Mexico and Texas, equivalent to
      an area of 1771/7 acres. --Bartlett.

   8. (Mining.) A stope or set of stopes. [Sp. Amer.]
      [Webster 1913 Suppl.]

   Syn: Work; toil; drudgery; task; exertion; effort; industry;
        painstaking. See Toll.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Labor \La"bor\, v. i. [imp. & p. p. Labored; p. pr. & vb. n.
   Laboring.] [OE. labouren, F. labourer, L. laborare. See
   Labor, n.] [Written also labour.]
   1. To exert muscular strength; to exert one's strength with
      painful effort, particularly in servile occupations; to
      work; to toil.
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            Adam, well may we labor still to dress
            This garden.                          --Milton.
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   2. To exert one's powers of mind in the prosecution of any
      design; to strive; to take pains.
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   3. To be oppressed with difficulties or disease; to do one's
      work under conditions which make it especially hard,
      wearisome; to move slowly, as against opposition, or under
      a burden; to be burdened; -- often with under, and
      formerly with of.
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            The stone that labors up the hill.    --Granville.
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            The line too labors, and the words move slow.
                                                  --Pope.
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            To cure the disorder under which he labored. --Sir
                                                  W. Scott.
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            Come unto me, all ye that labor and are heavy laden,
            and I will give you rest.             --Matt. xi. 28
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   4. To be in travail; to suffer the pangs of childbirth; to be
      in labor.
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   5. (Naut.) To pitch or roll heavily, as a ship in a turbulent
      sea. --Totten.
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The Collaborative International Dictionary of English v.0.48:

labour \la"bour\, n.
   Same as labor; -- British spelling. [Chiefly Brit.]
   [PJC]

WordNet (r) 3.0 (2006):

labour
    n 1: a social class comprising those who do manual labor or work
         for wages; "there is a shortage of skilled labor in this
         field" [syn: labor, labour, working class,
         proletariat]
    2: concluding state of pregnancy; from the onset of contractions
       to the birth of a child; "she was in labor for six hours"
       [syn: parturiency, labor, labour, confinement,
       lying-in, travail, childbed]
    3: a political party formed in Great Britain in 1900;
       characterized by the promotion of labor's interests and
       formerly the socialization of key industries [syn: British
       Labour Party, Labour Party, Labour, Labor]
    4: productive work (especially physical work done for wages);
       "his labor did not require a great deal of skill" [syn:
       labor, labour, toil]
    v 1: work hard; "She was digging away at her math homework";
         "Lexicographers drudge all day long" [syn: labor,
         labour, toil, fag, travail, grind, drudge,
         dig, moil]
    2: strive and make an effort to reach a goal; "She tugged for
       years to make a decent living"; "We have to push a little to
       make the deadline!"; "She is driving away at her doctoral
       thesis" [syn: tug, labor, labour, push, drive]
    3: undergo the efforts of childbirth [syn: labor, labour]