FIRKIN Meaning of FIRKIN in English n.1 a small cask for liquids, butter, fish, etc. 2 Brit. (as a measure) half a kilderkin (8 or 9 gallons). Etymology: ME ferdekyn, prob. f. MDu. vierdekijn (unrecorded) dimin. of vierde fourth Oxford English vocab. Оксфордский английский словарь. 2012