Of the very first, before anything derived from it. Of what was there when there was nothing else.
Latin primordialis (original, first of all), from primordium (beginning, origin): primus (first) + ordium, from ordiri (to begin, to lay the first thread of a web) — the same root order descends from.
Of what was there before anything derived from it existed. Naming a thing primordial is a claim about sequence, not about worth — it says only that nothing else came first.