Definitions for "Billon"
An alloy of gold and silver with a large proportion of copper or other base metal, used in coinage.
An alloy of bronze and silver. The silver content ranges from very high, so that the coin looks like silver, to very low, so that it looks like bronze.
A metal alloy occassionally used for minor coin issues consisting of a mixture of silver and a very high copper content. Sometimes billon coins are treated with a thin silver coating to give a shiny appearance.