Etymology

Noun

1. A varying measure of capacity, usually being the fourth part of a barrel; specifically, a measure equal to nine imperial gallons. [Eng.]
   • 1882, James Edwin Thorold Rogers, A History of Agriculture and Prices in England, Volume 4, p. 205:

     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.

2. A small wooden vessel or cask of indeterminate size, -- used for butter, lard, etc.
3. A weight measure for butter, equalling 56 pounds.