hypocoristic vs pen 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. 

pen name

noun

  • A fictitious name used by an author in place of their actual name; a writer's pseudonym. 

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