The Collaborative International Dictionary of English v.0.48:

Inverse \In*verse"\, a. [L. inversus, p. p. of invertere: cf. F.
   inverse. See Invert.]
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   1. Opposite in order, relation, or effect; reversed;
      inverted; reciprocal; -- opposed to direct.
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   2. (Bot.) Inverted; having a position or mode of attachment
      the reverse of that which is usual.
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   3. (Math.) Opposite in nature and effect; -- said with
      reference to any two operations, which, when both are
      performed in succession upon any quantity, reproduce that
      quantity; as, multiplication is the inverse operation to
      division. The symbol of an inverse operation is the symbol
      of the direct operation with -1 as an index. Thus sin-1 x
      means the arc or angle whose sine is x.
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   Inverse figures (Geom.), two figures, such that each point
      of either figure is inverse to a corresponding point in
      the order figure.

   Inverse points (Geom.), two points lying on a line drawn
      from the center of a fixed circle or sphere, and so
      related that the product of their distances from the
      center of the circle or sphere is equal to the square of
      the radius.

   Inverse ratio, or Reciprocal ratio (Math.), the ratio of
      the reciprocals of two quantities.

   Inverse proportion, or Reciprocal proportion, an equality
      between a direct ratio and a reciprocal ratio; thus, 4 : 2
      : : 1/3 : 1/6, or 4 : 2 : : 3 : 6, inversely.
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The Collaborative International Dictionary of English v.0.48:

Proportion \Pro*por"tion\, n. [F., fr. L. proportio; pro before
   + portio part or share. See Portion.]
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   1. The relation or adaptation of one portion to another, or
      to the whole, as respect magnitude, quantity, or degree;
      comparative relation; ratio; as, the proportion of the
      parts of a building, or of the body.
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            The image of Christ, made after his own proportion.
                                                  --Ridley.
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            Formed in the best proportions of her sex. --Sir W.
                                                  Scott.
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            Documents are authentic and facts are true precisely
            in proportion to the support which they afford to
            his theory.                           --Macaulay.
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   2. Harmonic relation between parts, or between different
      things of the same kind; symmetrical arrangement or
      adjustment; symmetry; as, to be out of proportion. "Let us
      prophesy according to the proportion of faith." --Rom.
      xii. 6.
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   3. The portion one receives when a whole is distributed by a
      rule or principle; equal or proper share; lot.
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            Let the women . . . do the same things in their
            proportions and capacities.           --Jer. Taylor.
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   4. A part considered comparatively; a share.
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   5. (Math.)
      (a) The equality or similarity of ratios, especially of
          geometrical ratios; or a relation among quantities
          such that the quotient of the first divided by the
          second is equal to that of the third divided by the
          fourth; -- called also geometrical proportion, in
          distinction from arithmetical proportion, or that in
          which the difference of the first and second is equal
          to the difference of the third and fourth.
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   Note: Proportion in the mathematical sense differs from
         ratio. Ratio is the relation of two quantities of the
         same kind, as the ratio of 5 to 10, or the ratio of 8
         to 16. Proportion is the sameness or likeness of two
         such relations. Thus, 5 to 10 as 8 to 16; that is, 5
         bears the same relation to 10 as 8 does to 16. Hence,
         such numbers are said to be in proportion. Proportion
         is expressed by symbols thus:
         [1913 Webster] a:b::c:d, or a:b = c:d, or a/b = c/d.
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      (b) The rule of three, in arithmetic, in which the three
          given terms, together with the one sought, are
          proportional.
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   Continued proportion, Inverse proportion, etc. See under
      Continued, Inverse, etc.

   Harmonical proportion or Musical proportion, a relation
      of three or four quantities, such that the first is to the
      last as the difference between the first two is to the
      difference between the last two; thus, 2, 3, 6, are in
      harmonical proportion; for 2 is to 6 as 1 to 3. Thus, 24,
      16, 12, 9, are harmonical, for 24:9::8:3.

   In proportion, according as; to the degree that. "In
      proportion as they are metaphysically true, they are
      morally and politically false." --Burke.
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