The Collaborative International Dictionary of English v.0.48:

Preponderate \Pre*pon"der*ate\, v. t. [imp. & p. p.
   Preponderated; p. pr. & vb. n. Preponderating.] [L.
   praeponderatus, p. p. of praeponderare; prae before +
   ponderare to weigh, fr., pondus, ponderis, a weight. See
   Ponder.]
   1. To outweigh; to overpower by weight; to exceed in weight;
      to overbalance.
      [1913 Webster]

            An inconsiderable weight, by distance from the
            center of the balance, will preponderate greater
            magnitudes.                           --Glanvill.
      [1913 Webster]

   2. To overpower by stronger or moral power.
      [1913 Webster]

   3. To cause to prefer; to incline; to decide. [Obs.]
      [1913 Webster]

            The desire to spare Christian blood preponderates
            him for peace.                        --Fuller.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Preponderate \Pre*pon"der*ate\, v. i.
   To exceed in weight; hence, to incline or descend, as the
   scale of a balance; figuratively, to exceed in influence,
   power, etc.; hence; to incline to one side; as, the
   affirmative side preponderated.
   [1913 Webster]

         That is no just balance in which the heaviest side will
         not preponderate.                        --Bp. Wilkins.
   [1913 Webster]

WordNet (r) 3.0 (2006):

preponderate
    v 1: weigh more heavily; "these considerations outweigh our
         wishes" [syn: preponderate, outweigh, overbalance,
         outbalance]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "preponderate":
   best, bestride, better, cap, dictate, dominate, domineer, exceed,
   excel, go one better, have the ascendancy, improve on, master,
   outweigh, overbalance, overbear, overcome, overpass, overtop,
   perfect, play first fiddle, predominate, prevail, reign,
   rule the roost, surpass, take the lead, top, tower above,
   tower over, transcend, trump, twist, wear the pants