simultaneity vs synchronism

simultaneity

noun
  • The quality or state of being simultaneous; simultaneousness. 

  • More than one complete musical texture occurring at the same time. This first appeared in the music of Charles Ives, and is common in the music of Conlon Nancarrow, and others. 

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