The term 'Bourbon Barrel' can be summarized by the crossword solution 'CASK, ' which is a four-letter word. A CASK is a barrel, usually made of wood, that is used for aging and storing alcoholic beverages such as whiskey and bourbon. The CASK is often charred on the inside to give the whiskey or bourbon a unique flavor. Bourbon barrels are typically made from American white oak and are used to age bourbon whiskey for at least two years.