intern vs pen in

intern

verb
  • To internalize. 

  • To work as an intern. Usually with little or no pay or other legal prerogatives of employment, for the purpose of furthering a program of education. 

  • To imprison somebody, usually without trial. 

  • To confine or hold (foreign military personnel who stray into the state's territory) within prescribed limits during wartime. 

noun
  • A student or recent graduate who works in order to gain experience in their chosen field. 

  • A medical student or recent graduate working in a hospital as a final part of medical training. 

  • A person who is interned, forcibly or voluntarily. 

pen in

verb
  • To enclose (animals) in a pen. 

  • To schedule; fix a date for. 

  • To cause to be stuck in a situation; to be forced into a situation by circumstances. 

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