Lewis & Short

Mĕdĭōmātrĭci, ōrum, m., a people of Gaul, on the Moselle, in the neighborhood of Metz, Caes. B. G. 4, 10.
Hence, Mĕdĭ-ōmātrĭcus, a, um, adj.
In sing., Inscr. Grut. 731, 12; and in fem., Inscr. Orell. 3523.