Royal dukedoms in the United Kingdom
In the British peerage, a royal duke is a member of the British royal family, entitled to the titular dignity of prince and the style of "His Royal Highness" who holds a dukedom. Dukedoms are the highest titles in the British roll of peerage and the holders of these particular dukedoms are Princes of the Blood Royal. The holders of the dukedoms are royal not the titles themselves. They are titles created and bestowed on legitimate sons and male-line grandsons of the British monarch, usually upon reaching their majority or marriage. The titles can be inherited but cease to be called "royal" once they pass beyond the grandsons of a monarch. As with any peerage, once the title becomes extinct, it may subsequently be recreated by the reigning monarch at any time.
Baronage
Eventually the duties of the executive office of earldom became redundant, being absorbed by the sheriff, and the title of earl became in itself a title of nobility above that of baron, yet the baronage remained the collective term for both degrees, since earls continued nonetheless to hold their lands "per baroniam". Possession of a barony was thus the common factor of the baronage. Indeed in the ancient sense of the word baron as simply a tenant-in-chief, all attendees at parliament were "peers", that is to say "equals" (Latin: "pares") one to the other in regard to their feudal standing under the king. With the decline of the feudal system and the creation of barons by writ from 1265, that is to say by a personal summons from the king based on the recipient's personal characteristics rather than his form of land tenure, the feudal barony lost its claim as the qualifying factor for nobility, and the barony by writ, or by letters patent from 1388, became altogether personal not territorial. The Further degrees of nobility of dukes, marquesses and viscounts were likewise created by writ and by patent, and the term baronage was no longer adequate to describe all degrees of nobility collectively. Thus was coined the term peerage to replace it.