Noun
troy weight
a system of units of weight/mass, mostly used for precious metals and gemstones, in which the pound contains 12 ounces which each contain 480 grains
Of these, the avoirdupois weight is the most common system used in the U.S., although Troy weight is still used to weigh precious metals. Source: Internet
Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. Source: Internet
Troy weight may take its name from the French market town of Troyes in France where English merchants traded at least as early as the early 9th century. Source: Internet