backset vs strike down

backset

verb
  • To plow again in the fall; said of prairie land broken up in the spring. 

noun
  • A check; a relapse; a discouragement; a setback. 

  • Whatever is thrown back in its course, such as water. 

strike down

verb
  • To knock down. 

  • To kill someone or something; to cause to die suddenly. 

  • To prostrate by illness. 

  • To invalidate (a law, statute etc.) 

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