The Collaborative International Dictionary of English v.0.48:

Independent \In`de*pend"ent\, a. [Pref. in- not + dependent: cf.
   F. ind['e]pendant.]
   [1913 Webster]
   1. Not dependent; free; not subject to control by others; not
      relying on others; not subordinate; as, few men are wholly
      independent.
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            A dry, but independent crust.         --Cowper.
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   2. Affording a comfortable livelihood; as, an independent
      property.
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   3. Not subject to bias or influence; not obsequious;
      self-directing; as, a man of an independent mind.
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   4. Expressing or indicating the feeling of independence;
      free; easy; bold; unconstrained; as, an independent air or
      manner.
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   5. Separate from; exclusive; irrespective.
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            That obligation in general, under which we conceive
            ourselves bound to obey a law, independent of those
            resources which the law provides for its own
            enforcement.                          --R. P. Ward.
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   6. (Eccl.) Belonging or pertaining to, or holding to the
      doctrines or methods of, the Independents.
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   7. (Math.) Not dependent upon another quantity in respect to
      value or rate of variation; -- said of quantities or
      functions.
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   8. (U. S. Politics) Not bound by party; exercising a free
      choice in voting with either or any party.
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   Independent company (Mil.), one not incorporated in any
      regiment.

   Independent seconds watch, a stop watch having a second
      hand driven by a separate set of wheels, springs, etc.,
      for timing to a fraction of a second.

   Independent variable. (Math.) See Dependent variable,
      under Dependent.

   Syn: Free; uncontrolled; separate; uncoerced; self-reliant;
        bold; unconstrained; unrestricted.
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The Collaborative International Dictionary of English v.0.48:

Variable \Va"ri*a*ble\, n.
   1. That which is variable; that which varies, or is subject
      to change.
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   2. (Math.) A quantity which may increase or decrease; a
      quantity which admits of an infinite number of values in
      the same expression; a variable quantity; as, in the
      equation x^2 - y^2 = R^2, x and y are variables.
      [1913 Webster]

   3. (Naut.)
      (a) A shifting wind, or one that varies in force.
      (b) pl. Those parts of the sea where a steady wind is not
          expected, especially the parts between the trade-wind
          belts.
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   Independent variable (Math.), that one of two or more
      variables, connected with each other in any way whatever,
      to which changes are supposed to be given at will. Thus,
      in the equation x^2 - y^2 = R^2, if arbitrary
      changes are supposed to be given to x, then x is the
      independent variable, and y is called a function of x.
      There may be two or more independent variables in an
      equation or problem. Cf. Dependent variable, under
      Dependent.
      [1913 Webster]

WordNet (r) 3.0 (2006):

independent variable
    n 1: (statistics) a variable whose values are independent of
         changes in the values of other variables [syn: independent
         variable, experimental variable]