Webster’s Revised Unabridged Dictionary · 1913
Triptych
Trip′tych (·tĭk), n. [Gr. τρίπτυχος consisting of three layers or plates; τρι (see Tri-) + πτύξ, πτυχός, a fold, layer.] Anything in three parts or leaves. Specifically: — (a) A writing tablet in three parts, two of which fold over on the middle part.
(b) A picture or altarpiece in three compartments.