duumvirate

Synonym of diarchy: rule by two people, especially two men.

To replace the all-powerful Salan, de Gaulle appointed a duumvirate – Paul Delouvrier and General Maurice Challe.

This was to raise the prospect of a duumvirate – ‘two heads in the same hat’, as Bernis quaintly put it.

Any of several offices of the Roman Republic held by two joint magistrates known as duumvirs.