A dominion or region ruled by a duke or duchess.

plural of duchy

The territory owned, ruled, or reigned over by a grand duke or grand duchess; contrast grand dukedom.

(historical) A duchy, encompassing the regions of Attica and Boeotia, which was established in Greece in 1205 after the conquest of the Byzantine Empire during the Fourth Crusade.

(historical) A mediaeval duchy in southern Italy, established in the 7th century CE as the Byzantine outpost Ducatus Neapolitanus; especially from 661, when Emperor Constans II appointed Basil I of Naples as the new dux (“military commander”).

A country, a duchy in Europe, now only composed of the Channel Islands in the English Channel; a crown possession of the Monarch of England, since the Conquest of England by William the Conqueror, Duke of Normandy; bureaucratically, it is administered by the in the United Kingdom

plural of grand duchy

The official name of the independent country of Luxembourg.

(historical) A former European state from the 13th century until 1795, encompassing the territory of modern-day Lithuania and Belarus, a large part of Ukraine, and small parts of Russia and Poland