tetrarchy
noun
te·trar·chy ˈte-ˌträr-kē 
ˈtē-
plural tetrarchies
: government by four persons ruling jointly
Example Sentences
Recent Examples on the Web Emperor Diocletian tried to bring order by distributing power to a four-ruler tetrarchy that would govern the four quarters of the empire. 
Kristin Baird Rattini, National Geographic, 25 Feb. 2019
Kristin Baird Rattini, National Geographic, 25 Feb. 2019 Word History
First Known Use
15th century, in the meaning defined above