reminisce vs retain

reminisce

verb
  • To remember fondly; to reminisce about. 

  • To recall the past in a private moment, often fondly or nostalgically. 

  • To talk or write about memories of the past, especially pleasant memories. 

noun
  • An act of reminiscence. 

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