serendipity vs stroke of fortune

serendipity

noun
  • The occurrence and development of events by chance in a happy or beneficial way. 

  • An unsought, unintended, and/or unexpected, but fortunate, discovery and/or learning experience that happens by accident. 

  • A combination of events which have come together by chance to make a surprisingly good or wonderful outcome. 

stroke of fortune

noun
  • Synonym of stroke of luck 

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