The Collaborative International Dictionary of English v.0.48:

Variable \Va"ri*a*ble\, a. [L. variabilis: cf. F. variable.]
   1. Having the capacity of varying or changing; capable of
      alternation in any manner; changeable; as, variable winds
      or seasons; a variable quantity.
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   2. Liable to vary; too susceptible of change; mutable;
      fickle; unsteady; inconstant; as, the affections of men
      are variable; passions are variable.
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            Lest that thy love prove likewise variable. --Shak.
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            His heart, I know, how variable and vain! --Milton.
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   Variable exhaust (Steam Eng.), a blast pipe with an
      adjustable opening.

   Variable quantity (Math.), a variable.

   Variable-rate mortgage (Finance), a mortgage whose
      percentage interest rate varies depending on some agreed
      standard, such as the prime rate; -- used often in
      financing the purchase of a home. Such a mortgage usually
      has a lower initial interest rate than a fixed-rate
      mortgage, and this permits buyers of a home to finance
      the purchase a house of higher price than would be
      possible with a fixed-rate loan.

   Variable stars (Astron.), fixed stars which vary in their
      brightness, usually in more or less uniform periods.
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   Syn: Changeable; mutable; fickle; wavering; unsteady;
        versatile; inconstant.
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WordNet (r) 3.0 (2006):

variable quantity
    n 1: a quantity that can assume any of a set of values [syn:
         variable, variable quantity]