Lewis & Short

octāvārĭus, a, um, adj. [octavus],

  1. I. of or belonging to the eighth part (post-class.): vectigal, a tax of the eighth part, Cod. Just. 7, 4, 65.
  2. II. Subst.: octāvārĭus, ĭi, m., a receiver of this tax: octavarii vectigal accipiant, Cod. Th. 4, 12, 8; cf. octavus, II. B.