citrus fruit vs grapefruit

citrus fruit

noun
  • Any of the fruits in the common genus Citrus of flowering plants in the family Rutaceae. 

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. 

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