Plutocracy is rule by the wealth

Wealth

Wealth is the abundance of valuable resources or material possessions. The word wealth is derived from the old English wela, which is from an Indo-European word stem...

y, or power provided by wealth. The combination of both plutocracy and oligarchy

Oligarchy

Oligarchy is a form of power structure in which power effectively rests with an elite class distinguished by royalty, wealth, family ties, commercial, and/or military legitimacy...

 is called plutarchy.

The word plutocracy (Modern Greek

Modern Greek

Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

: πλουτοκρατία - ploutokratia) is derived from the Ancient Greek

Ancient Greek

Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

 root ploutos, meaning wealth and kratos, meaning to rule or to govern.
The term plutocracy is generally used to describe these two distinct concepts: one of a historical nature and one of a modern political nature.