Lewis & Short

ad-nĕpos (atn-), ōtis, m., a son of the abnepos or of the abneptis, i. e. the grandson of a great-grandson, or of a greatgranddaughter, i. e. a fourth-grandson; corresponding in the descending line to atavus in the ascending. So in the epitaph of the emperor Commodus: DIVI NERVAE ADNEPOTI, Orell. Inscr. 887; so Dig. 38, 10, 1, § 7 al.