concomitance vs synchronism

concomitance

noun
  • occurrence or existence together or in connection with one another, coexistence 

  • A concomitant. 

  • The Roman Catholic doctrine of the existence of the entire body of Christ in the Eucharist, under each element, so that the body and blood are both received by communication in one kind only. 

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 concomitance and synchronism occurred in a corpus of books? (source: Google Ngram Viewer )