Hypostasis

That which forms the basis of anything; underlying principle; a concept or mental entity conceived or treated as an existing being or thing.

Substance; subsistence; essence; person; personality; -- used by the early theologians to denote any one of the three subdivisions of the Godhead, the Father, Son, and Holy Spirit.

Principle; an element; -- used by the alchemists in speaking of salt, sulphur, and mercury, which they considered as the three principles of all material bodies.

That which is deposited at the bottom of a fluid; sediment.

(metaphysics) essential nature or underlying reality