Lewis & Short

Thessălŏnīca, ae, or -ē, ēs, f., = Θεσσαλονίκη, a city of Macedonia, on the Sinus Thermaicus, now Saloniki, Mel. 2, 3, 1; Plin. 4, 10, 17, § 36; Cic. Planc. 41, 99; id. Q. Fr. 1, 4, 2; Liv. 39, 27 al.
Hence, Thessălŏnīcenses, ium, m., the inhabitants of Thessalonica, Cic. Prov. Cons. 2, 4; id. Pis. 34, 84.