knuckle under vs reject

knuckle under

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

reject

verb
  • To refuse a romantic advance. 

  • To refuse to accept. 

  • To block a shot, especially if it sends the ball off the court. 

noun
  • A rejected takeoff. 

  • A rejected defective product in a production line. 

  • Something that is rejected. 

  • An unpopular person. 

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