If you measure weight in pounds, and 16 ounces are in a pound, then you use the avoirdupois system. The word may not be as familiar to you as the names for measuring distance — the imperial system (feet, inches, yards, miles) and the metric system (based on meters) — but the avoirdupois system has been in use for centuries. The word comes from an Old French phrase, “aveir de peis,” meaning “goods of weight.” The word “avoirdupois” can also be used in a humorous context to refer to heaviness of weight in general; for example, “The dog has been getting too many treats, and his avoirdupois is showing it.”