Lewis & Short

Sēquăna, ae, f., one of the principal rivers of Gallia Celtica, the Seine, Caes. B. G. 1, 1; 7, 57; 7, 58; Mel. 3, 2, 4; masc., Plin. 4, 17, 31, § 105.
Hence,

    1. 1. Sēquă-ni, ōrum, m., the dwellers on the Sequana, Caes. B. G. 1, 1; 1, 2; 1, 9; 1, 10; 1, 31; 1, 35; 1, 44; 4, 10; 6, 12; 7, 66; Cic. Att. 1, 19, 2.
    2. 2. Sēquănus, a, um, adj., of or belonging to the Sequani: gens, Luc. 1, 425: ager, Plin. 14, 1, 3, § 18.
    3. 3. Sēquănī-cus, a, um, adj., of the Sequani: textrix. Mart. 4, 19, 1.