courgette vs zucchini

courgette

noun
  • The edible fruit of this marrow/squash. 

  • A particular variety of Cucurbita pepo, a small marrow/squash. 

zucchini

noun
  • The edible fruit of this variety of squash. 

  • A courgette; a variety of squash, Cucurbita pepo, which bears edible fruit. 

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