entertain vs retain

entertain

verb
  • To receive and take into consideration; to have a thought in mind. 

  • To have someone over at one's home for a party or visit. 

  • To amuse (someone); to engage the attention of agreeably. 

retain

verb
  • To keep in possession or use. 

  • 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 hold secure. 

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