occupy vs retain

occupy

verb
  • To fill or hold (an official position or role). 

  • To fill space. 

  • To fill. 

  • To live or reside in. 

  • To possess or use the time or capacity of; to engage the service of. 

  • To hold the attention of. 

  • To have, or to have taken, possession or control of (a territory). 

  • To place the theodolite or total station at (a point). 

retain

verb
  • To keep in one's pay or service. 

  • 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 possession or use. 

  • To hold secure. 

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