Lewis & Short

Trans-tĭbĕrīnus, a, um, adj., that is beyond the Tiber, Transtiberine: ambulator, Mart. 1, 42, 3.
Subst.: Transtĭ-bĕrīni, ōrum, m., those dwelling beyond the Tiber, Cic. Att. 12, 23, 3.