boroughmaster vs commissioner

boroughmaster

noun
  • The mayor, governor, or bailiff of a borough. 

commissioner

noun
  • An official in charge of a government department, especially a police force. 

  • Someone commissioned to perform certain duties. 

  • A member of a commission. 

  • Someone who commissions something. 

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