Troy/trɔɪ/ Definition 1 of 3Pro Tip 1/3Precise Measurement The troy system is used for accuracy in measuring precious items. The jeweler measured the diamonds in troy carats. Pro Tip 2/3Specific Usage Troy is not used for everyday items like groceries or postage. He knew not to use troy weight for measuring flour. Pro Tip 3/3Not for People The troy system applies to objects, not quantifying people or animals. You wouldn't say, 'She weighs 120 troy ounces.'