Select the most appropriate one-word substitution for the given group of words. 

A political system based on government by God.

Thearchy

The most appropriate one-word substitution for a political system based on government by God is thearchy.

• Gerontocracy is a government ruled by elders.
• Oligarchy is a government ruled by a small group of people.
• Monarchy is a government ruled by a single person, usually a king or queen.

The word thearchy is derived from the Greek words theos, meaning "god", and arche, meaning "rule". It is a form of government in which the ruler is believed to be divinely appointed or inspired. In theocratic societies, the laws and policies of the government are based on religious principles.