The Collaborative International Dictionary of English v.0.48:

Proportional \Pro*por"tion*al\, a. [L. proportionalis: cf. F.
   proportionnel.]
   1. Having a due proportion, or comparative relation; being in
      suitable proportion or degree; as, the parts of an edifice
      are proportional. --Milton.
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   2. Relating to, or securing, proportion. --Hutton.
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   3. (Math.) Constituting a proportion; having the same, or a
      constant, ratio; as, proportional quantities; momentum is
      proportional to quantity of matter.
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   Proportional logarithms, logistic logarithms. See under
      Logistic.

   Proportional scale, a scale on which are marked parts
      proportional to the logarithms of the natural numbers; a
      logarithmic scale.

   Proportional scales, compasses, dividers, etc.
      (Draughting), instruments used in making copies of
      drawings, or drawings of objects, on an enlarged or
      reduced scale.
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