continue vs retain

continue

verb
  • To remain in a given place or condition; to remain in connection with; to abide; to stay. 

  • To make a continuation bet. 

  • To retain (someone or something) in a given state, position, etc. 

  • To proceed with (doing an activity); to prolong (an activity). 

  • To make last; to prolong. 

  • To resume. 

  • To adjourn, prorogue, put off. 

noun
  • An option allowing the player to resume play after game over, when all lives have been lost, while retaining their progress. 

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