Lewis & Short

imperterrĭtus (inp-), a, um, adj. [2. in-perterritus; cf. Quint. 1, 5, 65], undaunted, unterrified (poet. and late Lat.), Verg. A. 10, 770; Sil. 14, 187; Ambros. in Psa. 37, § 50; Greg. M. in Job, 6, 38.