Dux

Lat. [from ducere, to lead.] A leader or military commander. In feudal and old European law. Duke; a title of honor, or order of nobility.

I Bl. Com. 397. Crabh*s Hist. 236.

The origin and history of this title are elaborately treated by Spelman, who observes that it was originally an official title, afterwards honorary, and finally feudal and hereditary. Hux is used in Bracton as descriptive of the first order of subjects in the kingdom. Sub eis [regibus'\ duces, comites, barones, <fec.; under them, dukes, earls, barons, &c. Bract, fol. 5 b.