concurrence vs concurrency

concurrence

noun
  • An instance of simultaneous occurrence. 

  • Agreement; concurring. 

concurrency

noun
  • The property or an instance of being concurrent; something that happens at the same time as something else. 

  • A property of systems where several processes execute at the same time. 

  • A stretch of road that is shared between two or more numbered or named routes. 

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