DUKE-DUKE, a quality given in Spain to a grandee of the house of Silva, on account of his having several duchies from the union of two considerable houses in his person. Don Roderigo de Silva, eldest son of Don Ruy Gomez de Silva, and heir of his duchies and principalities, having married the eldest daughter of the Duke de l'Infantado, the Duke de Pastrana, who was descended from her, added to his other great titles that of duke-duke, to distinguish himself from the other dukes, some of whom might enjoy several duchies, but none so considerable ones.