Īsis, is, and idis. f., = Ἶσις, the Egyptian goddess Isis, Cic. N. D. 3, 19, 47; Ov. M. 9, 772; Tac. G. 9; Luc. 9, 158.

— Hence, Isidis crinis, an unknown plant, Juba ap. Plin. 13, 25, 52, § 142.

— Isidis sidus, the planet Venus, Plin. 2, 8, 6, § 37.

— Deriv. Īsiacus, a, um, adj., = Ἰσιακός, of or belonging to Isis: conjectores, Enn. ap. Cic. Div. 1, 58, 132: focus, Ov. P. 1, 1, 52: Isiacae sacraria lenae, Juv. 6, 488.

—Subst.: Īsia-cus, i, m., a priest of Isis, Suet. Dom. 1; Val. Max. 7, 3, 8; Plin. 27, 7, 29, § 53 al.