commissioner vs pilot officer

commissioner

noun
  • Someone commissioned to perform certain duties. 

  • A member of a commission. 

  • Someone who commissions something. 

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

pilot officer

noun
  • The lowest rank of a commissioned officer in the RAF, equivalent to an Army ensign or coronet 

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