cop out vs retain

cop out

verb
  • To plead guilty and ask for mercy. 

  • To avoid or shirk, either by failing to perform, or by performing in a grossly insufficient, negligent, or superficial manner. 

retain

verb
  • 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. 

  • To hold secure. 

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