dollar vs piece of eight

dollar

noun
  • A quarter of a pound or one crown, historically minted as a coin of approximately the same size and composition as a then-contemporary dollar coin of the United States, and worth slightly more. 

  • Official designation for currency in some parts of the world, including Canada, the United States, Australia, New Zealand, Hong Kong, and elsewhere. Its symbol is $. 

  • Money generally. 

  • Imported from the United States, and paid for in U.S. dollars. (Note: distinguish "dollar wheat", North American farmers' slogan, meaning a market price of one dollar per bushel.) 

  • A unit of reactivity equal to the interval between delayed criticality and prompt criticality. 

piece of eight

noun
  • The peso, a silver coin that was minted in Spain and its colonies from the end of 15th century, equal to eight reales (hence the name). 

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