Oligarchy is a small number of people having power as opposed to plutocracy where only rich people hold power. So the difference between Oligarchy and Plutocracy comes to a few people's government versus rich people's government.
Oligarchy as a noun is a government run by only a few, often the wealthy. while Plutocracy as a noun is government by the wealthy.
Part of speech: noun
Definition: A government run by only a few, often the wealthy. Those who make up an oligarchic government. A state ruled by such a government.
Part of speech: noun
Definition: Government by the wealthy.A controlling class of the wealthy.
We hope you now know whether to use Oligarchy or Plutocracy in your sentence.