The Collaborative International Dictionary of English v.0.48:

Extension \Ex*ten"sion\, n. [L. extensio: cf. F. extension. See
   Extend, v. t.]
   1. The act of extending or the state of being extended; a
      stretching out; enlargement in breadth or continuation of
      length; increase; augmentation; expansion.
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   2. (Physics) That property of a body by which it occupies a
      portion of space.
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   3. (Logic & Metaph.)
      (a) Capacity of a concept or general term to include a
          greater or smaller number of objects; -- correlative
          of intension.
      (b) the class or set of objects to which a term refers; --
          contrasted with intension, the logical specification
          which defines members of a class, being the set of
          attributes which are necessary and sufficient to
          recognize an object as a member of the class.
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                The law is that the intension of our knowledge
                is in the inverse ratio of its extension. --Sir
                                                  W. Hamilton.
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                The extension of [the term] plant is greater
                than that of geranium, because it includes more
                objects.                          --Abp.
                                                  Thomson.
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   4. (Surg.) The operation of stretching a broken bone so as to
      bring the fragments into the same straight line.
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   5. (Physiol.) The straightening of a limb, in distinction
      from flexion.
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   6. (Com.) A written engagement on the part of a creditor,
      allowing a debtor further time to pay a debt.
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   Counter extension. (Surg.) See under Counter.

   Extension table, a table so constructed as to be readily
      extended or contracted in length.
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