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]

WordNet (r) 3.0 (2006):

preponderating
    adj 1: having superior power and influence; "the predominant
           mood among policy-makers is optimism" [syn: overriding,
           paramount, predominant, predominate,
           preponderant, preponderating]