Lewis & Short

Thĕŏpompos, i, m., = Θεόπομπος, a Greek historian and orator, a pupil of Isocrates, Cic. de Or. 2, 13, 57; 2, 23, 94; 3, 9, 36; Nep. Alcib. 11, 1.
Hence, Thĕŏ-pompēus or -īnus, a, um, adj., of or belonging to Theopompus, Theopompean: Theopompino genere (dicendi), Cic. Att. 2, 6, 2: Theopompeo more, id. Or. 61, 207.