break-off vs cave in

break-off

noun
  • That which breaks off, or is broken off 

  • A break, discontinuance, or interruption 

  • The first shot in a game of snooker or other cue-game 

verb
  • To play the first shot in a game of snooker 

cave in

noun
  • The act of something collapsing or caving in. 

  • The act of relenting. 

  • The location where something has caved in. 

verb
  • To collapse inward or downward. 

  • To relent; to grant approval against one's initial will. 

How often have the words break-off and cave in occurred in a corpus of books? (source: Google Ngram Viewer )