Jamieson, Fausset and Brown on Genesis 36:15-19

15-19. dukes--The Edomites, like the Israelites, were divided into tribes, which took their names from his sons. The head of each tribe was called by a term which in our version is rendered "duke"--not of the high rank and wealth of a British peer, but like the sheiks or emirs of the modern East, or the chieftains of highland clans. Fourteen are mentioned who flourished contemporaneously.