knuckle under vs nonconform

knuckle under

verb
  • To yield or cooperate when pressured or forced to do so. 

nonconform

noun
  • A manufactured product, etc. that fails to conform to the required standards. 

verb
  • To fail or refuse to conform; to differ. 

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