knuckle under vs rebel

knuckle under

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

rebel

verb
  • To resist or become defiant toward an authority. 

noun
  • Synonym of Confederate: a citizen of the Confederate States of America, especially a Confederate soldier. 

  • A person who resists an established authority, often violently. 

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