co-occurrence vs simultaneity

co-occurrence

noun
  • The fact of a thing occurring simultaneously with something else; correlation. 

  • An instance of a thing occurring simultaneously with something else; co-incidence. 

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. 

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