lord vs royal duke

lord

verb
  • Domineer or act like a lord. 

  • To invest with the dignity, power, and privileges of a lord; to grant the title of lord. 

noun
  • A peer of the realm, particularly a temporal one 

  • One possessing similar mastery in figurative senses (esp. as lord of ~) 

  • A magnate of a trade or profession. 

  • The heavenly body considered to possess a dominant influence over an event, time, etc. 

  • One possessing similar mastery over others; (historical) any feudal superior generally; any nobleman or aristocrat; any chief, prince, or sovereign ruler; in Scotland, a male member of the lowest rank of nobility (the equivalent rank in England is baron) 

  • A feudal tenant holding his manor directly of the king 

royal duke

How often have the words lord and royal duke occurred in a corpus of books? (source: Google Ngram Viewer )