knockback vs rejection

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. 

rejection

noun
  • The act of rejecting. 

  • The state of being rejected. 

  • An immune reaction of a host organism to a foreign biological tissue, such as in an organ transplant. 

  • A blocked shot. 

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