hypostasis (n.)

Greek word meaning "substance; subsistence;" from hypo "under, beneath" (see hypo-) + stasis "a standing, a position" (see stasis). Used in Ecclesiastical Greek since earliest times for "person" of God in the Trinity. This led to centuries of wrangling over the definition. "In the necessity they were under of expressing themselves strongly against the Sabellians, the Greeks made choice of the word hypostasis, and the Latins of persona ; which change proved the occasion of endless disagreement" ["Pantologia, A New Cabinet Cyclopaedia," London, 1819]. The same word in old medicine meant "sediment in the urine."