The Collaborative International Dictionary of English v.0.48:

Couple \Cou"ple\ (k[u^]p"'l), n. [F. couple, fr. L. copula a
   bond, band; co- + apere, aptum, to join. See Art, a., and
   cf. Copula.]
   1. That which joins or links two things together; a bond or
      tie; a coupler. [Obs.]
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            It is in some sort with friends as it is with dogs
            in couples; they should be of the same size and
            humor.                                --L'Estrange.
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            I'll go in couples with her.          --Shak.
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   2. Two of the same kind connected or considered together; a
      pair; a brace. "A couple of shepherds." --Sir P. Sidney.
      "A couple of drops" --Addison. "A couple of miles."
      --Dickens. "A couple of weeks." --Carlyle.
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            Adding one to one we have the complex idea of a
            couple.                               --Locke.
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            [Ziba] met him with a couple of asses saddled. --2
                                                  Sam. xvi. 1.
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   3. A male and female associated together; esp., a man and
      woman who are married or betrothed.
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            Such were our couple, man and wife.   --Lloyd.
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            Fair couple linked in happy, nuptial league.
                                                  --Milton.
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   4. (Arch.) See Couple-close.
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   5. (Elec.) One of the pairs of plates of two metals which
      compose a voltaic battery; -- called a voltaic couple or
      galvanic couple.
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   6. (Mech.) Two rotations, movements, etc., which are equal in
      amount but opposite in direction, and acting along
      parallel lines or around parallel axes.
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   Note: The effect of a couple of forces is to produce a
         rotation. A couple of rotations is equivalent to a
         motion of translation.
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