asynchronism vs simultaneity

asynchronism

noun
  • Synonym of asynchrony 

simultaneity

noun
  • 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. 

  • The quality or state of being simultaneous; simultaneousness. 

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