Puncheon: a large cask for liquids, particularly alcoholic drinks, holding 72 to 120 gallons. It can also mean (according to the Concise Oxford Dictionary) a short post, especially a support for a roof in a coal mine.
Nancy and Peggy carry a small barrel of polished oak in Amazon. Peggy tells Roger that it was meant as a water breaker, because our natives thought the water in the lake wasn’t fit to drink .... but we always drink it, not straight out of the lake, but boiled for tea, and so we use the water breaker as a puncheon for feastable drinks. They carry the barrel slung from an oar for portage and swig the lemonade. Titty says I never tasted better rum (SA11).