a unit of capacity, used esp for alcoholic beverages. It has several values, being 54 imperial gallons in the case of beer and 52.5 imperial gallons in the case of wine
2.
a large cask used for shipment of wines and spirits
late 14c., presumably on some perceived resemblance. The original liquid measure was 63 old wine gallons (by a statute of 1423); later anywhere from 100 to 140 gallons. Borrowed into other Germanic languages, oddly, as ox-head (cf. Du. okshoofd, Ger. oxhoft, Swed. oxhufvud).