diva vs vocalist

diva

noun
  • Any female celebrity, usually a well known singer or actress. 

  • A person who may be considered or who considers herself (or by extension himself) much more important than others, has high expectations of others and who is extremely demanding and fussy when it comes to personal privileges. 

vocalist

noun
  • A singer; a person who likes to sing. 

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