hypocoristic vs tropical yam

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. 

tropical yam

noun
  • Synonym of name (yam) 

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