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Traditionally, a cooper is someone who makes wooden staved vessels, bound together with hoops and possessing flat ends or heads. Examples of a cooper's work include but are not limited to casks, barrels, buckets, tubs, butter churns, hogsheads, firkins, tierces, rundlets, puncheons, pipes, tuns, butts, pins and breakers.
The word is derived from Middle Dutch kūpe "basket, wood, tub" and may ultimately stem from cupa, the Latin word for vat. Everything a cooper produces is referred to collectively as cooperage. A cask is any piece of cooperage containing a bouge, bilge, or bulge in the middle of the container. A barrel is technically a measure of the size of a cask, so the term "barrel-maker" cannot be used synonymously with "cooper." The facility in which casks are made is also referred to as a cooperage.
Traditionally there were four divisions in the cooper's craft. The "dry" or "slack" cooper made containers that would be used to ship dry goods such as cereals, nails, tobacco, fruits and vegetables. The "dry-tight" cooper made casks designed to keep dry goods in and moisture out. Gunpowder and flour casks are examples of a "drytight" cooper's work. The "white cooper" made straight staved containers like washtubs, buckets and butter churns, that would hold water and other liquids, but did not allow shipping of the liquids. Usually there was no bending of wood involved in white cooperage. The "wet" or "tight" cooper made casks for long-term storage and transportation of liquids that could even be under pressure, as with beer.
Today, coopers mostly operate barrel-making machinery and assemble casks for the wine and spirits industry.
While plastics, stainless steel, pallets, and corrugated cardboard have replaced most wooden containers and largely made the cooper obsolete, there is still demand for high-quality wooden barrels, and it is thought that the highest-quality barrels are those hand-made by professional coopers. Examples may be seen in the cooperage at Seguin Moreau, a cooperage which was incorporated into the House of Rémy in 1971 for the express purposes of providing barrels made of Limousin oak. Limousin oak is renowned for the rich vanilla-like flavor it imparts to cognac. Rémy Martin will then produce Rémy Martin Grand Cru in these barrels with a retail cost well in excess of USD $1500 per bottle,, a single barrel being expected to hold nearly a quarter of a million dollars worth of cognac.
Coffin-makers are also sometimes known as coopers, though this is an uncommon usage.
Cooperage as a namesake 
In much the same way that the profession of smithing produced the common English surname Smith and the German name Schmidt, the trade of cooperage also gave the English name Cooper, French name Tonnelier and Tonnellier, Greek name Βαρελάς/Varelas, Danish name Bødker, German names like Faßbinder (literally cask binder), Böttcher (tub maker), Scheffler and Kübler, Dutch names like Kuiper or Cuypers, the Latvian name Mucenieks, the Hungarian name Kádár, Bodnár, Polish names such as Bednarz, Bednarski or Bednarczyk, the Czech name Bednář, the Romanian names Dogaru and Butnaru, Ukrainian family name Bondarenko, Ukrainian/Russian family name Bondarev and Bocharov, the Jewish name Bodner and the Portuguese names Tanoeiro and Toneleiro, Spanish Cubero and Macedonian Bacvarovski (Македонски: Бачваровски) and Italian "Bottai" (from "botte").