knockback vs refutation

knockback

noun
  • A rejection; a refusal. 

  • A blow that causes the recipient to fall or move backwards, a knock back; a recoil. 

  • Something that impedes or reverses progress; a setback. 

refutation

noun
  • A vocal answer to an attack on one's assertions. 

  • An act of refuting or disproving; the disproving of an argument, opinion, testimony, doctrine or theory by argument or countervailing proof; evidence of falseness. 

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