Shokudo or zokudo is a penalty charge which was paid with copper (or money) to a government official in an amount that corresponds to the crime in exchange for imprisonment.
贖銅（しょくどう、ぞくどうとも言う）は、実刑の代わりに罪相当額の銅（ないし財貨）を官司へ納入する換刑であった。