DUKE (Dux), a sovereign prince, without the title or quality of king. The word is borrowed from the Latin through the medium of the modern Greek. Some sovereigns have the title of grand duke, as the Grand Duke of Tuscany and the Grand Duke of Muscovy. The title of grand duke belongs to the heir apparent of Russia; and the title of archduke is given to all the sons of the house of Austria, and that of archduchess to all the daughters.