chili pepper vs chilli 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.) 

chilli pepper

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