troy weight

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A system of units of weight in which the grain is the same as in the avoirdupois system and the pound contains 12 ounces, 240 pennyweights, or 5,760 grains.

from The Century Dictionary.

• noun A weight chiefly used in weighing bread, silk, gold, silver, and articles of jewelry, but now only for gold and silver.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a system of weights used for precious metals and gemstones; based on a 12-ounce pound and an ounce of 480 grains