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.