knockback vs thumbs down

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. 

thumbs down

noun
  • A rejection or refusal. 

  • A gesture signifying disapproval; a thumb pointing down out of a fist. 

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