The English word "cay" comes from the Spanish word "cayo" and this from the Taíno word "cayo" meaning "small island". The English words "key" and "quay" (which means wharf) come from the old French "kai" meaning "sand bank". Because it is a Taíno word, "cay" (and the other forms) are used mainly in the Caribbean, but the type of island is found in the tropical seas where there are coral reefs.