Lewis & Short

octāvus, a, um, adj. [octo],

  1. I. the eighth: octava pars, Cic. Att. 15, 26, 4: legio, Caes. B. G. 2, 23: marmor, the eighth mile-stone, Mart. 9, 65, 4.
  2. II. Subst.: octāva, ae, f.
    1. A. (Sc. hora.) The eighth hour of the day, Mart. 4, 8, 5; Juv. 1, 49.
    2. B. (Sc. pars.) The eighth part, as a tax, Cod. Just. 4, 65, 7; Cod. Th. 4, 12, 6; Ulp. Fragm. 6, 12 (cf. octavarius).
  3. III. Adv.: octāvum, for the eighth time, Liv. 6, 36, 7.