diptych

noun8

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. •
   A picture or series of pictures painted on two tablets, usually connected by hinges.
3. •
   A novel published in two volumes forming one continuous story (as opposed to a duology or dilogy).
4. •
   A literary work consisting of two contrasting parts, such as a narrative telling the same story from two opposing points of view.
5. •
   Any work made up of two parts treating complementary or contrasting aspects of one general topic.

   • “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
6. •
   (historical) 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.
7. •
   A double catalogue, containing in one part the names of living, and in the other of deceased, ecclesiastics and benefactors of a church.
8. •
   A catalogue of saints.