Lewis & Short

armentārĭus, a, um, adj. [armentum],

  1. I. pertaining to a herd of cattle: morbi, Sol. 11: equiso, App. M. 7.
    Hence,
  2. II. Subst.: armentārĭus, ii, m.
    1. A. A herdsman, neat-herd, * Lucr. 6, 1252; Varr. R. R. 2, 5, 18: omnia secum Armentarius Afer agit, Verg. G. 3, 344: armentarius ego sum, * Vulg. Amos, 7, 14.
    2. B. A surname of the emperor Galerius Maximianus, whose ancestors were shepherds, Aur. Vict. Ep. 40.