a quality or title of honour given to princes.—The kings of England and Spain had formerly no other title but that of highness; the first till the time of James I. and the second till that of Charles V. The petty princes of Italy began first to be complimented with the title of highness in the year 1630.—The duke of Orleans assumed the title of royal highness in the year 1631, to distinguish himself from the other princes of France.

The duke of Savoy, afterwards king of Sardinia, bore the title of royal highness, on account of his pretensions to the kingdom of Cyprus.—It is said that duke only took the title of royal highness, to put himself above the duke of Florence, who was called great duke; but the great duke afterwards assumed the title of royal highness, to put himself on a level with the duke of Savoy.

The prince of Conde first took the title of most serene highness, leaving that of simple highness to the natural princes.