knockback vs repulse

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. 

repulse

noun
  • refusal, rejection or repulsion 

  • the act of repulsing or the state of being repulsed 

verb
  • To repel or drive back. 

  • To reject or rebuff. 

  • To cause revulsion in. 

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