The term 'Horse-Chestnut' is often used to refer to the tree of the same name, which is native to Europe and parts of Asia. It is also commonly known as the 'Conker' tree, which is a 6-letter word derived from the same term. The Horse-Chestnut tree produces a spiky, inedible fruit that is popularly used in the game of conkers, where two players take turns hitting each other's fruits with their own until one breaks.