chicken out vs concede

chicken out

verb
  • To shy away from a daring task; to decline, refuse, or avoid something due to fear or uncertainty. 

concede

verb
  • To yield or suffer; to surrender; to grant 

  • To admit or agree to be true; to acknowledge. 

  • To yield or make concession. 

  • (of a bowler) to have runs scored off of one's bowling. 

  • To grant, as a right or privilege; to make concession of. 

  • To have a goal or point scored against 

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