cave in vs relent

cave in

verb
  • To collapse inward or downward. 

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

noun
  • The act of relenting. 

  • The location where something has caved in. 

  • The act of something collapsing or caving in. 

relent

verb
  • To slacken; to abate. 

  • To give in or be swayed; to become less hard, harsh, or cruel; to show clemency. 

noun
  • Stay; stop; delay. 

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