Learn English – the opposite of the “sub” prefix

Meta- comes from Ancient Greek, and in this sense means beyond, with, about or after. An example is Aristotle's Metaphysics which his editors placed after his Physics, and started readers thinking it might mean more than location. That suggests to me that the Latin pre- or Greek pro- could be possible antonyms used in a similar way.

But this would only help if people used it. Shall we try to push premetadata or prometadata? Or would actual data be more easily understood?

In conceptual modelling, where we study whole/part relationships, we would call that the whole.

A more technical name would be root.