Lewis & Short

Tarbelli, ōrum, m., a people in Aquitanian Gaul, extending southwards from Burdigala to the Pyrenees, in the neighborhood of the mod. Dax, Caes. B. G. 3, 27; Plin. 4, 19, 33, § 108; 31, 2, 2, § 4.
Hence,

  1. A. Tarbellus, a, um, adj., Tarbellian: Pyrene, Tib. 1, 7, 9: mater, Aus. Parent. 2, 2.
  2. B. Tarbellĭus, a, um, adj., Tarbellian: aequor, Luc. 1, 421.
  3. C. Tar-bellĭcus, a, um, adj., Tarbellian: Aturus, i. e. the river Adour, Aus. Mos. 468: arva, id. Ep. 24, 125: origo, id. Prof. 16, 7.