(in Britain and Canada) a mixture of alcohol and water or an alcoholic beverage that contains 49.28 per cent of alcohol by weight, 57.1 per cent by volume at 51°F: up until 1980 used as a standard of alcoholic liquids
2.
(in the US) a similar standard mixture containing 50 per cent of alcohol by volume at 60°F
proof spirit in American English
an alcoholic liquor, or a mixture of alcohol and water, containing by volume 50 percent (in Great Britain and Canada 57.10 percent) ethyl alcohol at 15.6°C (c. 60°F)