acquiesce vs cave in

acquiesce

verb
  • To concur upon conviction; to assent to; usually, to concur, not heartily but so far as to forbear opposition. 

  • To rest satisfied, or apparently satisfied, or to rest without opposition and discontent (usually implying previous opposition or discontent); to accept or consent by silence or by omitting to object. 

cave in

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

  • To collapse inward or downward. 

noun
  • The act of relenting. 

  • The location where something has caved in. 

  • The act of something collapsing or caving in. 

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