Lewis & Short

Prŏpontis (Prōpontis, Manil. 4, 676), ĭdos and ĭdis, f., = Προποντίς,

  1. I. the Propontis or Sea of Marmora, between the Hellespont and the Thracian Bosporus, Mel. 1, 1, 5; 1, 3, 1; Plin. 4, 12, 24, § 76; Liv. 38, 16; Tac. A. 2, 54; Flor. 3, 6; Cat. 4, 9; Ov. P. 4, 9, 118.
    Hence,
  2. II. Prŏpontĭăcus, a, um, adj., of or belonging to the Propontis: aqua, Prop. 3 (4), 21, 1: orae, Ov. Tr. 1, 10, 29.