Definition of "diptych"

diptych

/ˈdɪptɪk/

noun
plural diptychs
1. A writing tablet consisting of two leaves of rigid material connected by hinges and shutting together so as to protect the writing within.
2. (art) A picture or series of pictures painted on two tablets, usually connected by hinges.
3. (Christianity) A double catalogue, containing in one part the names of living, and in the other of deceased, ecclesiastics and benefactors of a church.
4. (Christianity) A catalogue of saints.
5. (historical, Ancient Rome) Artistically-wrought tablets distributed by consuls, etc. of the later Roman Empire to commemorate their tenure of office; hence (transferred sense) a list of magistrates.
6. A novel published in two volumes forming one continuous story (as opposed to a duology or dilogy).
7. A literary work consisting of two contrasting parts, such as a narrative telling the same story from two opposing points of view.
  Quotations
  A very simple narrative, a diptych, a pastoral in which the author narrates the birth of Christ […] first as it has impressed the rich countryman Asveer, then as it has been seen by the skeptic Nicodemus.
  1942, François Closset, “Review of Bejegegning van Christus by G. Walschap”, in Books Abroad, volume 16, number 2, page 202
8. (transferred sense) Any work made up of two parts treating complementary or contrasting aspects of one general topic.
  Quotations
  “Vegetation of the Sonoran Desert” is the first volume of a diptych “Vegetation and Flora of the Sonoran Desert,” for which Ira L. Wiggins is to write the companion volume on the flora.
  1954, Frank E. Egler, “Forrest Shreve and the Sonoran Desert”, in Geographical Review, volume 44, number 1, page 138