1300-50;Middle English: melted mass of gold or silver < Anglo-Latinbulliōn- (stem of bulliō) in same sense (< Anglo-Frenchbullion mint), literally, a boiling, equivalent to bull(īre) to bubble, boil1 + -iōn--ion
early 15c., "uncoined gold or silver," from Anglo-Norm. bullion "bar of precious metal," also "place where coins are made, mint," perhaps, through the notion of "melting," from O.Fr. boillir "to boil," from L. bullire "boil." But perhaps it is rather from O.Fr. bille "stick, block of wood."