let go vs run in

let go

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

  • 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. 

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

  • To gain weight 

run in

verb
  • To score (a try). 

  • To arrest; (especially) to track down and arrest. 

  • To insert (a word, etc.) without making a line break or new paragraph (so that it is not free-hanging). 

  • To use new machinery at less than full speed, preventing damage. 

  • To start a new regime slowly. 

  • To use new machinery at less than full speed, preventing damage. (transitive sense) 

  • To alter the position of matter to fill vacant space. 

adj
  • (sometimes comparable) Having been run in to seat the parts. 

  • (not comparable) Having been run in before or behind previous text. 

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