retain vs retrospect

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. 

retrospect

verb
  • To look or refer back to; to reflect on. 

noun
  • Consideration of past times. 

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