disapproval vs knockback

disapproval

noun
  • The act of disapproving; condemnation. 

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. 

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