opus vs periodical

opus

noun
  • A work of music or set of works with a specified rank in an ordering of a composer's complete published works. 

  • A work, especially of art. 

periodical

noun
  • A regularly issued thematic publication that contains the most current information in its field, often the primary means for communication of original scholarship or creative work at the cutting edge of research in its field. 

  • A publication issued regularly, but less frequently than daily. 

adj
  • Periodic. 

  • Published at regular intervals of more than one day, especially weekly, monthly, or quarterly. 

  • Of, or relating to such a publication. 

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