bonus vs piece of good fortune

bonus

verb
  • To pay a bonus, premium 

noun
  • An extra sum given as a premium, e.g. to an employee or to a shareholder. 

  • Something extra that is good; an added benefit. 

  • An addition to the player's score based on performance, e.g. for time remaining. 

  • One or more free throws awarded to a team when the opposing team has accumulated enough fouls. 

piece of good fortune

How often have the words bonus and piece of good fortune occurred in a corpus of books? (source: Google Ngram Viewer )