puncheon

An English measure of capacity for wine, one third of a tun. This unit is also called a firkin or tertian. After 1824 it = 70 imperial gallons, about 318.2 liters. Previously it had been 84 wine gallons. See wine barrel for a chart showing its relationship to other wine measures.

It also had other conventional commercial values, for particular commodities:

Mid 19th century, according to Waterston¹:

brandy	100 to 110 imperial gallons
molasses	1,120 to 1,344 pounds av.
rum	90 to 100 imperial gallons
Scotch whiskey	112 to 120 imperial gallons

Lederer speculates that the 18th century American pon, a cask in which sugar was shipped, was a shortening of puncheon.²

2.
Richard M. Lederer, Jr.
Colonial American English. A Glossary.
Essex, Connecticut: A Verbatim Book, 1985.