Lewis & Short

Serdica, ae, f., a city of Mœsia, Cassiod. Hist. Eccl. 4, 21.
Hence,

  1. A. Ser-dicensis, e, adj., Serdican, of Serdica: concilium, Cassiod. Hist. Eccl. 4, 24.
  2. B. Serdicēnus, a, um, adj., Serdican, of Serdica, Cassiod. Hist. Eccl. 4, 33; 4, 38.