The Collaborative International Dictionary of English v.0.48:

Multiply \Mul"ti*ply\, v. t. [imp. & p. p. Multiplied; p. pr.
   & vb. n. Multiplying.] [F. multiplier, L. multiplicare, fr.
   multiplex manifold. See Multitude, Complex.]
   1. To increase in number; to make more numerous; to add
      quantity to.
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            Impunity will multiply motives to disobedience.
                                                  --Ames.
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   2. (Math.) To add (any given number or quantity) to itself a
      certain number of times; to find the product of by
      multiplication; thus 7 multiplied by 8 produces the number
      56; to multiply two numbers. See the Note under
      Multiplication.
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   3. To increase (the amount of gold or silver) by the arts of
      alchemy. [Obs.]
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   Multiplying gear (Mach.), gear for increasing speed.

   Multiplying lens. (Opt.) See under Lens.
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The Collaborative International Dictionary of English v.0.48:

Multiply \Mul"ti*ply\, v. i.
   1. To become greater in number; to become numerous.
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            When men began to multiply on the face of the earth,
            and daughters were born unto them.    --Gen. vi. 1.
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   2. To increase in extent and influence; to spread.
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            The word of God grew and multiplied.  --Acts xii.
                                                  24.
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   3. To increase amount of gold or silver by the arts of
      alchemy. [Obs.] --Chaucer.
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WordNet (r) 3.0 (2006):

multiply
    adv 1: in several ways; in a multiple manner; "they were
           multiply checked for errors" [ant: singly]
    v 1: combine by multiplication; "multiply 10 by 15" [ant:
         divide, fraction]
    2: combine or increase by multiplication; "He managed to
       multiply his profits" [syn: multiply, manifold]
    3: have young (animals) or reproduce (organisms); "pandas rarely
       breed in captivity"; "These bacteria reproduce" [syn:
       breed, multiply]
    4: have offspring or produce more individuals of a given animal
       or plant; "The Bible tells people to procreate" [syn:
       reproduce, procreate, multiply]