mandarin orange vs shaddock

mandarin orange

noun
  • A small citrus tree (Citrus reticulata) with fruit resembling the orange. 

  • The fruit of this tree, smaller than an orange and oblate. In daily usage, it may include other similar citrus fruits like Citrus unshiu (satsuma or mikan) Citrus tangerina (tangerine). 

shaddock

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

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