An alloy of copper and silver where copper predominates, historically used to make coins; also in British English, a million millions (a trillion in American English).
From Old French 'bille' (ingot) or possibly from Latin 'bis' (twice). In numeral sense, from French 'bi-' (two) plus '-llion,' originally meaning a million million in the long scale.
Billon coins allowed medieval mints to stretch precious silver by mixing it with cheaper copper—literally the inflation of medieval times, where the word 'billon' itself means something is debased or mixed.
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