pairing vs simultaneousness

pairing

noun
  • The combination or union of two things. 

  • An agreement between two members of a legislative body holding opposite opinions to refrain from voting, so that both may absent themselves. 

simultaneousness

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

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