Lewis & Short

Āternus, i, m., = Ἄτερνος, a river in Samnium emptying into the Adriatic Sea, now Pescara, Plin. 3, 5, 6, § 44; 3, 12, 17, § 106.
At its mouth was the town Āter-num, i, n., = Ἄτερνον, named after it, now also called Pescara, Liv. 24, 47; cf. Mann. Ital. I. p. 468.
Hence, Aternensis ager, Front. Col. p. 120 Goes.