symmetallism

noun

sym·​met·​al·​lism (ˌ)si(m)-ˈme-tə-ˌli-zəm 

: a system of coinage in which the unit of currency consists of a particular weight of an alloy of two or more metals

Word History

Etymology

syn- + -metallism (as in bimetallism)

First Known Use

circa 1895, in the meaning defined above