Ounce

An ounce (abbreviated oz; apothecary symbol: ℥) is a unit of mass used in some systems of measurement.

Whilst various definitions have been used throughout history, two remain in common use: the avoirdupois ounce equal to approximately 28.3 g and the troy ounce of about 31.1 g. The avoirdupois ounce is widely used as part of the United States customary and British imperial systems, but the troy ounce is now only commonly used for the mass of precious metals such as gold.

Etymology

Ounce derives from Latin uncia, a unit that was one twelfth (¹⁄₁₂) of the Roman pound (libra). Ounce was borrowed twice: first into Old English as ynsan or yndsan from an unattested Vulgar Latin form with ts for c before i (palatalization) and second into Middle English through Anglo-Norman and Middle French (unce, once, ounce). The abbreviation oz came later from the cognate Italian word onza (now spelled oncia).

Inch comes from the same Latin word, but differs because it was borrowed into Old English and underwent i-mutation or umlaut (u → y) and palatalization (k → ch).