congruency vs synchronism

congruency

noun
  • The state of being congruent 

  • The quality of agreeing; being suitable and appropriate 

synchronism

noun
  • The state of being synchronous. 

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

  • A temporal relationship between events. 

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