noun an obsolete British unit of capacity equal to 18 Imperial gallons.
Examples
“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.”