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1.                 From The Collaborative International Dictionary of English v.0.48:
                   
   
   
                   
                     
   Invariant \In*va"ri*ant\, n. (Math.)
      An invariable quantity; specifically, a function of the
      coefficients of one or more forms, which remains unaltered,
      when these undergo suitable linear transformations. --J. J.
      Sylvester.
      [1913 Webster]