The Collaborative International Dictionary of English v.0.48:

Multiplier \Mul"ti*pli`er\, n. [Cf. F. multiplier. Cf.
   Multiplicator.]
   1. One who, or that which, multiplies or increases number.
      [1913 Webster]

   2. (Math.) The number by which another number (the
      multiplicand) is multiplied. See the Note under
      Multiplication.
      [1913 Webster]

   3. (Physics) An instrument for multiplying or increasing by
      repetition or accumulation the intensity of a force or
      action, as heat or electricity. It is particularly used to
      render such a force or action appreciable or measurable
      when feeble. See Thermomultiplier.
      [1913 Webster]

WordNet (r) 3.0 (2006):

multiplier
    n 1: the number by which a multiplicand is multiplied [syn:
         multiplier, multiplier factor]