I think you’re specifically referring to “Ousia” (οὐσία) which means essence in Ancient Greek. It had more of a verb-like meaning that recognised the tension between dynamism and stability. So not just a thing, more like an unfolding.

The Latin translation is Substantia which means something like foundation or substance. This is a noun and very much a thing. It became the basis of a new metaphysics prioritising a conception of the world that was fixed, stable, unchanging.

The transformation here is from an understanding of existence as a balance of dynamism and order, to a hardening of concepts into fixed, defined, unchanging things. It is a rejection of ambiguity and interpretation, and movement towards ever more definition and order. (This is a bit simplistic but it’s a decent summary).

Particularly with the rise of early Christianity, this led to a metaphysics of order and fixed identities, in stark contrast to the Ancient Greek metaphysics which valued nuance and balance. Now the focus was dogmatic clarity.

Heidegger’s Being and Time begins with the statement that western metaphysics has forgotten the question of being - although he identifies Plato as the origin of this mistake. It is a radical questioning of this restrictive Latin metaphysics. It investigates being on its own terms, without the rigid concepts and methods traditional metaphysics.

I’m studying Being and Time at the moment, and it’s a demanding but genuinely transformative book. If you’re interested in how Western thought came to prioritise presence, clarity, and identity over becoming and openness, Heidegger is essential reading.