1. a form of government in which power is held by two rulers or authorities
Usage: also spelled diarchy; formal, political term

Examples

• The ancient Spartan system was a dyarchy, with two kings ruling simultaneously.
• Some scholars describe the British constitutional arrangement as a dyarchy between Parliament and the Crown.
• The dyarchy of the two consuls was a defining feature of the Roman Republic.
• Historical dyarchies often led to conflicts when the two rulers disagreed on policy.