isochronous vs periodical

isochronous

adj
  • Happening at regular intervals; isochronal. 

  • Happening at the same time; simultaneous. 

  • of or pertaining to data associated with time-sensitive applications. 

  • Of or pertaining to the use of clocks derived from the same clock reference. 

periodical

adj
  • Periodic. 

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

  • Of, or relating to such a publication. 

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. 

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