Definify.com
Webster 1913 Edition
Firkin
1.
A varying measure of capacity, usually being the fourth part of a barrel; specifically, a measure equal to nine imperial gallons.
[Eng.]
2.
A small wooden vessel or cask of indeterminate size, – used for butter, lard, etc.
[U.S.]
Webster 1828 Edition
Firkin
FIRKIN
,Noun.
A measure of capacity, being the fourth part of a barrel. It is nine gallons of beer, or eight gallons of ale, soap or herrings. In America, the firkin is rarely used, except for butter or lard, and signifies a small vessel or cask of indeterminate size, or of different sizes, regulated by the statutes of the different states.