Diarchy
Diarchy (or dyarchy) is a form of government where two people are usually the heads of state. The word comes from the Greek δι- "two elements" and ἀρχή, "rule" (from ἄρχω; -αρχία is a derived suffix). The term duumvirate is a hyponym (from Latin duumvirātus, "male diarchy") but some people use it erroneously for women.