A government where power is shared by four people, especially (historical) the Herodian tetrarchy established in Judea after the death of Herod and the Tetrarchy of Diocletian which ruled the Roman Empire in the years 293-313.
The land ruled by such a government, either together or separately.
A group of twenty people, especially (politics) a council of twenty men sharing an office or rule and particularly (historical) such an administrative council in ancient Rome.