a measure of quantity; half a kilderkin; as a small cask for liquids, fish, butter, etc.
Examples: firkin of ale [8 gallons]; of beer [9 gallons]; of butter [9 gallons]; of eels [10 1/2 gallons]; of herrings [8 gallons]; of marlvoisie [‘malmsey wine’]; of mead; of salmon, [10 1/2 gallons].