Fidius, ii, m. 1. fides, a surname of Jupiter, in Dionys. Halic. called Ζεὺς Πίστιος, identical with the Sabine Sancus: Nonas Sanco Fidione referrem, Ov. F. 6, 213; more usually connected with deus (dius) or medius (i. e. dius or deus, with the demonstr. part. me), and also joined into one word, mediusfidius, as an asseveration, qs. by the god of truth! as true as heaven! most certainly! itaque domi rituis nostri, qui per deum Fidium jurare vult, prodire solet in compluvium, Varr. ap. Non. 494, 30; cf. id. L. L. 5, § 66 Mull.: per deum Fidium quaeris, Plaut. As. 1, 1, 8: unum medius fidius tecum diem libentius posuerim, quam, etc., Cic. Fam. 5, 21, 1: quam mediusfidius veram licet cognoscas, Sall. C. 35, 2: non mediusfidius ipsas Athenas (loqui) tam Atticas dixerim, Plin. Ep. 4, 3, 5; Quint. 5, 12, 17 al.; cf. Paul. ex Fest. p. 147, 8 Mull.

— Of Hercules, Tert. Idol. 20; cf. Serv. ad Verg. A. 4, 204.