Why is a chilli called a chilli when it's hot?

We couldn't answer this question last week, but I'm pleased to tell you that Jose Fernandez in Mexico City has been listening to us on the internet. He says that the name comes from the Spanish word 'chile', which has its own roots respectively in the Nahuatl language (the Aztecs spoke a variant of this). So a chilli was originally called chile in Nahuatl. The Spanish then took this into their own language and the English language borrowed it from them. So the fact it is called a chilli has nothing to do with its temperature at all - it's just the word that was originally used for it in another language.