Gresham's law

Etymology
Named in 1858 by Henry Dunning Macleod, after Sir Thomas Gresham (1519–1579), English financier during the Tudor dynasty.

Proper noun

 * 1) An economic principle stating that, when a government overvalues one type of money and undervalues another, the undervalued money will leave the country or disappear from circulation into hoards, while the overvalued money will flood into circulation; or "bad money drives out good".