Bullion, a term applied to the gold and silver of the mines brought to a standard of purity. The word appears in an English act of 1336 in the French form "puissent sauvement porter à les exchanges ou bullion ... argent en plate, vessel d'argent, etc."; and apparently it is connected with bouillon, the sense of "boiling" being transferred in English to the melting of metal, so that bullion in the passage quoted meant "melting-house" or "mint." The first recorded instance of the use of the word for precious metal as such in the mass is in an act of 1451. From the use of gold and silver as a medium of exchange, it followed that they should approximate in all nations to a common degree of fineness; and though this is not uniform even in coins, yet the proportion of alloy in silver, and of carats alloy to carats fine in gold, has been reduced to infinitesimal differences in the bullion of commerce, and is a prime element of value even in gold and silver plate, jewelry, and other articles of manufacture.
Bullion, whether in the form of coins, or of bars and ingots stamped, is subject, as a general rule of the London market, not only to weight but to assay, and receives a corresponding value.