diptych

Concise Oxford English Dictionary © 2008 Oxford University Press:
diptych /ˈdɪptɪk/

▶noun

• 1 a painting, especially an altarpiece, on two hinged wooden panels which may be closed like a book.

• 2 an ancient writing tablet consisting of two hinged leaves with waxed inner sides.

– origin C17: via late L. from late Gk diptukha ‘pair of writing tablets’, neut. pl. of Gk diptukhos ‘folded in two’.