piece of good fortune vs windfall

piece of good fortune

windfall

noun
  • Something that has been blown down by the wind. 

  • A fruit that has fallen from a tree naturally, as from wind. 

  • A sudden large benefit; especially, a sudden or unexpected large amount of money, as from lottery or sweepstakes winnings or an unexpected inheritance or gift. 

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