bethink vs retain

bethink

verb
  • To think of (something or somebody) or that (followed by clause); to remind oneself, to consider, to reflect upon. 

  • To meditate, ponder; to consider. 

  • To determine, resolve. 

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 bethink and retain occurred in a corpus of books? (source: Google Ngram Viewer )