1) Dyarchy 2) Form of government 3) Political system 1) Dyarchy 
Diarchy (or dyarchy; from the Greek δι- / δύο meaning `two` and ἄρχω meaning `to rule`) is a form of government in which two individuals (`diarchs`) are joint heads of state. Most diarchs hold their position for life, passing the position to their children or other family members. Diarchy is one of the oldest forms of government: e...
government by two people
• (n.) A form of government in which the supreme power is vested in two persons.
Di'arch·y noun [ Greek 
diarchy, duarchy A government by two rulers.
dyarchy noun a form of government having two joint rulers
government in which power is vested in two rulers or authorities.