concurrence vs synchronism

concurrence

noun
  • An instance of simultaneous occurrence. 

  • Agreement; concurring. 

synchronism

noun
  • A temporal relationship between events. 

  • The tabular arrangement of contemporary events etc. in history. 

  • The state of being synchronous. 

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