Diptych
Object made of two paired flat plates, often joined by a hinge
A diptych (, DIP-tick) is any object with two flat plates which form a pair, often attached by a hinge. For example, the standard notebook and school exercise book of the ancient world was a diptych consisting of a pair of such plates that contained a recessed space filled with wax. Writing was accomplished by scratching the wax surface with a...