chile pepper vs chili pepper

chile pepper

chili pepper

noun
  • Any fruit of a plant of the botanical genus Capsicum, which has a spicy/burning flavour because it contains capsaicin. (Not all chili peppers are particularly spicy, but all true chili peppers contain some capsaicin, in contrast to e.g. the bell pepper, which is not a true chili pepper and does not.) 

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