dyarchy

/D AY1 ER0 K IY0/
noun
  1. 1

    Rule by two people.

  2. 2

    A state under the rule of two people.

    โ€œSwaziland is an absolute diarchy, ruled jointly by a king and a queen mother.โ€

Source: https://en.wiktionary.org/wiki/diarchy, https://en.wiktionary.org/wiki/dyarchy