hypostasis
noun[L. hypostasis; Gr. to stand.]
Properly, subsistence or substance. Hence it is used to denote distinct substance, or subsistence of the Father, Son, and Holy Spirit, in the Godhead, called by the Greek christians, three hypostases. The Latins more generally used persona to express the sense of hypostasis, and this is the modern practice. We say, the Godhead consists of three persons.