Metaproblem: Metadata vs Metadatum for a single data point?

Hi, non-native English speaker here. For some reason we have started to wonder what would be correct grammatically and what of these would you write in code? We have never seen a single piece of metadata written as metadatum in code. But we still wonder … just the important questions of life you know?

It is always "data" even if it is a single data point. metadata = MetaData[] still_metadata = metadata[0]

We should use datum. Because it's the singular of data. metadata = MetaDatum[] metadatum = metadata[0]

Thanks for clarification.