There are cases where zero-based indexing is more natural than one-based indexing. An example is naming the centuries: It would be nicer if this were called the twentiethan century instead of the twenty-first. When people talk about the fifteenth century, I have to think for a bit to understand what they mean. As such, I propose adding a suffix "an" to the end of any ordinal number to indicate a zero-based convention is being used -- this century would then be the twentiethan century [twεntiθən] as well as the twenty-first. A bit like degrees vs radians.