diptych vs missal

diptych

noun
  • A catalogue of saints. 

  • A picture or series of pictures painted on two tablets, usually connected by hinges. 

  • 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. 

  • A novel published in two volumes forming one continuous story (as opposed to a duology or dilogy). 

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

  • A writing tablet consisting of two leaves of rigid material connected by hinges and shutting together so as to protect the writing within. 

  • Any work made up of two parts treating complementary or contrasting aspects of one general topic. 

  • A literary work consisting of two contrasting parts, such as a narrative telling the same story from two opposing points of view. 

missal

noun
  • A book containing the prayers and responses needed when celebrating the Roman Catholic Mass throughout the year. 

  • A prayer book. 

How often have the words diptych and missal occurred in a corpus of books? (source: Google Ngram Viewer )