An ancient country and former province of the Roman Empire lying south and west of the River Danube, in present-day Austria, Hungary, Slovenia, and Croatia. It lost its separate identity after the Romans withdrew at the end of the 4th century.
Definition of Pannonia in US English:
Pannonia
proper nounpəˈnōnēə
An ancient country of southern Europe that was south and west of the Danube River, in present-day Austria, Hungary, Slovenia, and Croatia.