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

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.

(metaphysics) essential nature or underlying reality

(as defined here, in the Plotinian sense) underlying Divine or Absolute Reality, the Truth or Foundation or Essence or Support or Cause of a thing more

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.

(Suppositum). A complete and individual substance which has subsistence, i.e., a substance which is self-contained and autonomous ( sui juris) in its operations.

any of the three persons of the Godhead constituting the Trinity especially the person of Christ in which divine and human natures are united

a singular essence (ousia) subsisting in its independent being, numerically one, separate from others by its accidents