Source : Webster's Revised Unabridged Dictionary (1913)

Diptych \Dip"tych\, n. [L. diptycha, pl., fr. Gr. ? folded,
   doubled; di- = di`s- twice + ? to fold, double up.]
   1. Anything consisting of two leaves. Especially:
      (a) (Roman Antiq.) A writing tablet consisting of two
          leaves of rigid material connected by hinges and
          shutting together so as to protect the writing within.
      (b) A picture or series of pictures painted on two tablets
          connected by hinges. See {Triptych}.

   2. A double catalogue, containing in one part the names of
      living, and in the other of deceased, ecclesiastics and
      benefactors of the church; a catalogue of saints.

Source : WordNet®

diptych
     n : a painting or carving (especially an altarpiece) on two
         panels (usually hinged like a book)