Lewis & Short

exortīvus, a, um, adj. [2. exortus].

  1. I. Of or belonging to the rising of the heavenly bodies, ascendant (post-Aug.): mensura, Plin. 7, 49, 50, § 160.
  2. II. Transf., towards the sunrise, eastern: pars, Plin. 18, 34, 77, § 338: Oceanus, id. 37, 2, 11, § 39.
    In the neutr. plur. subst.: Narbonensis Galliae exortiva, the eastern part, Plin. 6, 34, 39, § 215.