DUKE, (Dux), a sovereign prince, without the title or quality of king. Such are the dukes of Lorraine, of Holstein, of 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 archduke is given to all the sons of the house of Austria, as that of archduchess to all the daughters.