tertĭārĭus — Lewis & Short
tertĭārĭus, a, um, adj.id.,
I containing a third part.
I Adj.:
stannum,that contains one part of white and two of black lead, Plin. 34, 17, 48, § 160. —
II Subst.: tertĭārĭum, ii, n., a third part, a third, Cato, R. R. 95, 1; Vitr. 4, 7, 5.