Lewis & Short

2. Issus or -os, i, f., = Ἰσσός,

  1. I. a city of Cilicia, on the Mediterranean (the Gulf of Issus, now Gulf of Iskenderun), at the foot of Mount Amanus, where Darius was defeated by Alexander, Mel. 1, 13, 1; Plin. 5, 27, 22, § 91; Cic. Fam. 2, 10, 3; Curt. 3, 8, 8.
  2. II. Deriv. Issĭcus, a, um, adj., of or belonging to Issus: sinus, the Gulf of Issus, Mel. 1, 13, 1; Plin. 2, 108, 112, § 243.