banker's bill vs greenback

banker's bill

greenback

noun
  • The United States dollar. 

  • A unit of American currency issued during the Civil War by the Treasury Department. 

  • A wave that has not yet begun to break. 

  • Any bill that is legal tender in the US (originally printed with green and black ink) issued by the Federal Reserve. 

How often have the words banker's bill and greenback occurred in a corpus of books? (source: Google Ngram Viewer )