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Căystrŏs or -us, i, m., = Κάϋστρος, a river in Lydia, which rises in Mount Tmolus, and falls into the sea at Ephesus, celebrated for the great number of its swans, now Kara-Su: Caystros, Ov. M. 5, 386; Mel. 1, 17, 2: Caystrus, Sen. Q. N. 4, 2, 19; Verg. G. 1, 384; Prop. 3 (4), 22, 15; Ov. M. 2, 253; Plin. 5, 29, 31, § 115.
Hence, Căy-strĭus, a, um, adj., of Caystros: ales = cygnus, Ov. Tr. 5, 1, 11.