back down vs ward off

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. 

ward off

verb
  • To parry, or turn aside. 

  • To avert or prevent. 

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