expel vs retain

expel

verb
  • To deport. 

  • To eject or erupt. 

  • To remove from membership. 

retain

verb
  • To hold secure. 

  • To employ by paying a retainer. 

  • To hold back (a pupil) instead of allowing them to advance to the next class or year. 

  • To keep in one's pay or service. 

  • To keep in possession or use. 

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