n. That which underlies something else; that which forms the basis of something; foundation; support.n. In theology, a person of the Trinity; one of the three real and distinct subsistences in the one undivided substance or essence of God.n. In metaphysics, a substantial mode by which the existence of a substantial nature is determined to subsist by itself and be in communicable; subsistence.n. A hypothetical substance; a phenomenon or state of things spoken and thought of as if it were a substance.n. Principle: a term applied by the alchemists to mercury, sulphur, and salt, in accordance with their” doctrine that these were the three principles of all material bodies.n. In medicine: A sediment, as of the urine; any morbid deposition in the body.n. An overfullness of blood-vessels caused by a dependent position, as of the veins of the legs (varicose veins), etc.; hypostatic congestion. Also hypostasy.