diptych

1. (art) A picture or series of pictures painted on two tablets, usually connected by hinges.

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

3. (Christianity) A catalogue of saints.

4. (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.Ancient-Romehistorical

5. (transferred sense) Any work made up of two parts treating complementary or contrasting aspects of one general topic.Examples: "“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."