amass vs let go

amass

verb
  • To collect into a mass or heap. 

  • to gather a great quantity of; to accumulate. 

  • To accumulate; to assemble. 

let go

verb
  • To gain weight 

  • To dismiss from employment. 

  • To release from one's grasp; to go from a state of holding on to a state of no longer holding on. 

  • To ignore (a comment, etc.). 

  • To emotionally disengage or to distract oneself from a situation. 

  • To fail to maintain a standard of appearance, behavior, or performance. 

  • Used other than figuratively or idiomatically: see let, go. 

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