chili pepper vs chilli pepper

chili pepper and chilli pepper both are nouns.

Word	Noun	Adjective	Verb	Adverb
chili pepper	Yes	No	No	No
chilli pepper	Yes	No	No	No

As nouns, chili pepper and chilli pepper are synonyms defined as:

chili pepper and chilli pepper: plant bearing very hot and finely tapering long peppers; usually red

Other synonyms of chili pepper include Capsicum annuum longum, cayenne, cayenne pepper, jalapeno, long pepper.

chili pepper (noun)	chilli pepper (noun)
very hot and finely tapering pepper of special pungency	plant bearing very hot and finely tapering long peppers; usually red
plant bearing very hot and finely tapering long peppers; usually red