grapefruit vs sweet lemon

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. 

sweet lemon

noun
  • A plant of the species Citrus medica (syn. Citrus limetta) or its fruit. 

  • Any of several plants that produce fruit resembling lemon or lime, but less acidic than lemon. 

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