Greenbacks, a name given to the inconvertible paper currency issued in the United States during the Civil War, so called from the colour of the notes, bonds, &c.; the name has since been popularly applied to the paper money of the States; the notes were made convertible in 1879.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Green, Thomas Hill * Greenland