kilderkin

kilderkin A small barrel.
An old English liquid measure, usually being half a barrel; containing 18 English beer gallons, or nearly twenty-two gallons, United States measure.
1882: 23 Hen. VIII, cap. 4... The barrel of beer is to hold 36 gallons, the kilderkin 18 gallons the firkin 9. But the barrel, kilderkin, and firkin of ale are to contain 32, 16, and 8 gallons. — James Edwin Thorold Rogers, A History of Agriculture and Prices in England, Volume 4, p. 205.