hypocoristic vs pet name

hypocoristic

noun
  • A nickname, especially one indicating intimacy and formed through a shortening of the original name. 

adj
  • Relating to a nickname, usually indicating intimacy with the person. 

  • Relating to baby talk. 

pet name

noun
  • A nickname, especially a name used by those in love with one another. 

  • Used other than figuratively or idiomatically: see pet, name. 

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