Lewis & Short

2. Ărī̆us (Arr-), i, m., = Ἀρεῖος or Ἄριος, a renowned heretic, also Ārĭus, Prud. Psych. 794.
Hence, Ărīānus, a, um, adj., pertaining to Arius, Arian, Hier. adv. Lucif. 7.Ărīāni, ōrum, m., the followers of Arius, the Arians, Hier. adv. Lucif. 7; Aug. Haeres. 49.