The Collaborative International Dictionary of English v.0.48:

Plutocrat \Plu"to*crat\, n.
   One whose wealth gives him power or influence; one of the
   plutocracy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plutocrat
    n 1: someone who exercises power by virtue of wealth

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "plutocrat":
   Daddy Warbucks, billionaire, bloated plutocrat, capitalist,
   fat cat, man of means, man of substance, man of wealth,
   millionaire, moneybags, moneyed man, multimillionaire, nabob,
   parvenu, rich man, richling, warm man, wealthy man