(Εὐστάθιος), a Greek physician in the latter half of the fourth century after Christ, to whom two of the letters of St. Basil are addressed. A. D. 373, 374. (vol. iii. Epist. 151, 189, ed. Bened.) In some MSS. he is called by the title "Archiater." The second of these letters is by some persons attributed to St. Gregory of Nyssa, and is accoringly printed in the third volume of his works, p. 6, &c., ed. Bened.