1. A sovereign prince; a ruler of a duchy.
2. The first order of nobility in Great Britain below the royal family.
“But after the Norman conquest, which changed the military policy of the nation, the kings themselves continuing for many generations dukes of Normandy, they would not honour any subjects with that title, till the time of Edward III; who, claiming to be the king of France, and thereby losing the ducal in the royal dignity, in the eleventh year of his reign created his son, Edward the black prince, duke of Cornwall: and many, of the royal family especially, were afterwards raised to the honour. However, in the reign of queen Elizabeth, A.D. 1572, the whole order became utterly extinct: but it was revived about fifty years afterwards by her successor, who was remarkably prodigal of honours, in the person of George Villiers duke of Buckingham.” 1 William Blackstone, Commentaries on the Laws of England 385 (1765).