- A measurement of the alcohol content of liquor.
Probably the 15th century. From Old French, preuve, meaning to prove. Earlier to Late Latin proba, meaning to test. The modern Russian word, proba, also has the same meaning.
Yes, this word actually has a nautical origin. The term comes from the practice of testing shipments of rum by customs officers. A sample of rum would be taken and lit with a match. If it burned, then it was “up to proof,” or about 50% alcohol by volume. This technique was apparently used until the invention of the hydrometer in the 17th century.
Still in use today, in the United States, the alcohol proof of a beverage is twice the percentage of Alcohol By Volume (ABV). For example, a whiskey or bourbon might have up to 160 proof, or 80% ABV.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic, CT: Mystic Seaport Museum.