repay vs reward

repay

verb
  • To make worthwhile; to yield a result worth the effort. 

  • Synonym of pay back in all senses. 

reward

verb
  • To recompense. 

  • To give a reward to or for. 

noun
  • Something of value given in return for an act. 

  • A prize promised for a certain deed or catch 

  • The result of an action, whether good or bad. 

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