diarchy(n = noun.group) dyarchy - a form of government having two joint rulers; Array
is a kind of form of government, political system

diarchy, n. (also dyarchy) (pl. -ies)
1 government by two independent authorities (esp. in India 1921-37).
2 an instance of this.

Derivative:
diarchal adj. diarchic adj.

Etymology:
DI-(1) + Gk -arkhia rule, after monarchy