Lewis & Short

Belgae, ārum, m., = Βέλγαι [Balge, in Lower Germany, a low, swampy region],

  1. I. the Belgians, a warlike people, of German and Celtic origin, in the north of Gaul, Caes. B. G. 1, 1; 2, 4; Mel. 3, 2, 4; Tac. A. 1, 43; 3, 40; id. H. 4, 17; 4, 76 al.
    In sing.: Bel-ga, ae, m., a Belgian, Luc. 1, 426; Claud. Laud. Stil. 1, 226.
  2. II. Deriv.: Belgĭ-cus, a, um, adj., Belgic: esseda, Verg. G. 3, 204: color, Prop. 2 (3), 18, 26: calami, Plin. 16, 36, 65, § 161: canis, Sil. 10, 80.
    Hence, Gallia Belgica, or absol. Belgica, the northern part of Gaul, between the Rhine, Seine, Marne, and the North Sea, inhabited by the Belgians, Plin. 4, 17, 31, § 105; 7, 16, 17, § 76.
    Absol., Plin. 15, 25, 30, § 103; Tac. H. 1, 12; 1, 58 al.