burghmaster vs mayor of the palace

burghmaster

noun
  • A burgomaster. 

  • An officer who directs and lays out the meres or boundaries for the workers. 

mayor of the palace

noun
  • In the Merovingian kingdoms, the king’s steward and, by the 7th century, de facto regent. 

How often have the words burghmaster and mayor of the palace occurred in a corpus of books? (source: Google Ngram Viewer )