burgomaster vs mayoress

burgomaster

noun
  • The mayor, or head magistrate, of a town in the Netherlands, Belgium, Germany and certain other countries. 

mayoress

noun
  • A female mayor. 

  • The wife of a (male) mayor. 

  • A daughter or female friend of a male mayor chosen by him to hold the title mayoress. 

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