Lewis & Short

Vātī̆cānus (i short, Hor. C. 1, 20, 7, but lengthened in Juv. and Mart.), a, um, adj. (sc. mons, collis), the Vatican Hill in Rome, on the western bank of the Tiber, Hor. C. 1, 20, 7; Juv. 6, 344; Fest. p. 379 Müll.; cf. Becker, Antiq. 1, p. 659 sq.; also plur., for the hill and the space around it: montes Vaticani, Cic. Att. 13, 33, 4: campus, id. ib.: ager, id. Agr. 2, 35, 96: vallis, between the Vatican and the Janiculum, Tac. A. 4, 14: Circus, Plin. 16, 40, 76, § 201: Vaticana (sc. vina), Vatican wine (a very inferior sort), Mart. 6, 92, 3; 10, 45, 5; cf. cadus, id. 1, 19, 2; 12, 48, 14.
Subst.: in Vaticano, Plin. 8, 14, 14, § 37; 16, 44, 87, § 237; 18, 3, 4, § 20: Vaticanus, the divinity presiding over the Vatican, Varr. ap. Gell. 16, 17, 2; Aug. Civ. Dei, 4, 8, 12.