don vs professor

don

noun
  • An employee of a university residence who lives among the student residents. 

  • A mafia boss. 

  • Any man, bloke, dude. 

  • A university professor, particularly one at Oxford or Cambridge. 

verb
  • To put on clothing; to dress (oneself) in an article of personal attire. 

professor

noun
  • The most senior rank for an academic at a university or similar institution, informally also known as "full professor." 

  • A teacher or faculty member at a college or university regardless of formal rank. 

  • A pianist in a saloon, brothel, etc. 

  • The puppeteer who performs a Punch and Judy show; a Punchman. 

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