Noun

1. A small barrel of no certain dimensions. It may contain from 3 to 20 gallons.
2. A measure for liquids, as for wine, usually 18.5 gallons.

   1882, Again, by 28 Hen. VIII, cap. 14, it is re-enacted that the tun of wine should contain 252 gallons, a butt of Malmsey 126 gallons, a pipe 126 gallons, a tercian or puncheon 84 gallons, a hogshead 63 gallons, a tierce 41 gallons, a barrel 31.5 gallons, a rundlet 18.5 gallons. — James Edwin Thorold Rogers, A History of Agriculture and Prices in England, p. 205.