Lewis & Short

Phĭlippi, ōrum, m., = Φίλιπποι, a city in Macedonia, on the borders of Thrace, celebrated for the battle in which Octavianus and Antony defeated Brutus and Cassius, now Filibi, Mel. 2, 2, 9; Liv. Epit. 124; Vell. 2, 70, 1; Flor. 4, 7; Vulg. Phil 1, 1.
Hence,

  1. A. Phĭ-lippensis, e, adj., of or belonging to Philippi, Philippian: Philippense bellum, Suet. Aug. 9: proelium, the battle of Philippi, Plin. 7, 45, 46, § 148: Brutus, who fell at Philippi, id. 34, 8, 19, § 82.
  2. B. Phĭlip-pēus, a, um, adj., of or belonging to Philippi, Philippian: campi, Vell. 2, 86, 2; Manil. 1, 906.
  3. C. Phĭlippĭcus, a, um, adj., of or belonging to Philippi, Philippian: in Philippicis campis, Plin. 33, 3, 12, § 39; Flor. 4, 2, 43.
  4. D.Phĭlippĭānus, a, um, adj., Philippian: cohortes, i. e. who fought at Philippi, Inscr. Maff. Mus. Ver. 325.