back down vs disprove

back down

verb
  • To withdraw from a commitment or position. 

  • To take a less aggressive position in a conflict than one previously has or has planned to. 

disprove

verb
  • To prove to be false or erroneous; to confute; to refute. 

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