What does the word "Plutonomy" mean?

From the link: http://www.investopedia.com/terms/p/plutonomy.asp#axzz1rId3JAnh

Definition of 'Plutonomy'
Economic growth that is powered and consumed by the wealthiest upper class of society. Plutonomy refers to a society where the majority of the wealth is controlled by an ever-shrinking minority; as such, the economic growth of that society becomes dependent on the fortunes of that same wealthy minority.

'Plutonomy' explained:
This buzz word was initially coined by analysts at Citigroup in 2005 to describe the incredible growth of the U.S. economy during that period despite increasing interest rates, commodity prices and an inflated national debt. Citigroup analysts argued that as such an economy continues to grow in the face of contradictory elements, the more important the society's ultra rich become to maintaining such growth. The analysts also believed that in addition to  U.S.A., other countries like Canada, Great Britain and China are also becoming plutonomies.