DUKE, Dux, a sovereign prince, without the title or quality of king. Such are the Duke of Lorraine, of Holstein, Savoy, of Parma, &c. The word is borrowed from the modern Greeks, who call ducas what the Latins call dux.
There are also two sovereigns who bear the title of grand-duke; as the grand-duke of Tuscany, and the grand-duke of Muscovy, now called the czar or emperor of Russia. The title of great duke belongs to the apparent heir of Russia; and the title of arch-duke is given to all the sons of the house of Austria, as that of arch-duchess to all the daughters.