simultaneity vs synchronicity

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. 

synchronicity

noun
  • The state of being synchronous or simultaneous. 

  • Coincidences that seem to be meaningfully related; supposedly the result of "universal forces". 

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