The Collaborative International Dictionary
Troy \Troy\, n. Troy weight.
Troy weight, the weight which gold and silver, jewels, and the like, are weighed. It was so named from Troyes, in France, where it was first adopted in Europe. The troy ounce is supposed to have been brought from Cairo during the crusades. In this weight the pound is divided into 12 ounces, the ounce into 20 pennyweights, and the pennyweight into 24 grains; hence, the troy ounce contains 480 grains, and the troy pound contains 5760 grains. The avoirdupois pound contains 7000 troy grains; so that 175 pounds troy equal 144 pounds avoirdupois, or 1 pound troy = 0.82286 of a pound avoirdupois, and 1 ounce troy = 117/175 or 1.09714 ounce avoirdupois. Troy weight when divided, the pound into 12 ounces, the ounce into 8 drams, the dram into 3 scruples, and the scruple into 20 grains, is called apothecaries' weight, used in weighing medicines, etc. In the standard weights of the United States, the troy ounce is divided decimally down to the 1/10000 part.
Wiktionary
n. 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
WordNet
n. a system of weights used for precious metals and gemstones; based on a 12-ounce pound and an ounce of 480 grains [syn: troy]
Wikipedia
Troy weight is a system of units of mass customarily used for precious metals and gemstones. There are 12 troy ounces per troy pound, (373.24 g) rather than the 16 ounces per pound (453.59 g) found in the more common avoirdupois system. The troy ounce is 480 grains, compared with the avoirdupois ounce, which is grains. Both systems use the same grain defined by the international yard and pound agreement of 1959 as exactly 0.064 798 91 gram. Although troy ounces are still used to weigh gold, silver, and gemstones, troy weight is no longer used in most other applications.
Usage examples of "troy weight".
The avoirdupois ounce contains 18 pennyweights 5 1/2 grains troy weight.
On the other hand, they have been used to weigh their money and medicine with the pennyweights and grains troy weight, and are not in the habit of using the pounds and ounces of that series.
That the ancient and modern Roman pound, containing 5256 grains of Troy weight, is about one twelfth lighter than the English pound, which is composed of 5760 of the same grains.
The gold was somewhat unorthodox, it having been captured in small uneven ingots which the Gibraltar goldsmiths had cast into smooth shining disks each marked 13oz Troy: one hundred and thirty grains Troy weight: but the silver and copper were in their usual homely forms.