Emily Dickinson Lexicon

FIR-KIN, n. [fur'kin; The first syllable is probably the Dan. fire, D. vier, four, and the latter as in kilderkin.]

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.