grapefruit vs shaddock

grapefruit

noun
  • The tree of the species Citrus paradisi, a hybrid of pomelo (Citrus maxima) and sweet orange. 

  • The large spherical tart fruit produced by this tree. 

shaddock

noun
  • Synonym of pomelo, in all its senses including (inexact) grapefruit. 

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