apprentice vs professor

apprentice

noun
  • A trainee, especially in a skilled trade. 

  • One who is bound by indentures or by legal agreement to serve a tradesperson, or other person, for a certain time, with a view to learn the art, or trade, in which his master is bound to instruct him. 

verb
  • To put under the care and supervision of a master, for the purpose of instruction in a trade or business. 

  • To be an apprentice to. 

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 apprentice and professor occurred in a corpus of books? (source: Google Ngram Viewer )