Lewis & Short

distermĭnus, a, um, adj. [dis-terminus],

  1. I. separated, divided: Tartessos latis distermina terris, Sil. 5, 399.
  2. II. Act., separating, parting.
    As subst.: distermĭna, ae, f. (sc. linea), the diameter, diagonal, Mart. Cap. 6, § 714.