Lewis Short
(adjective) : tertĭārĭus, a, um, id.
* Containing a third part.
* Adj.: stannum,that contains one part of white and two of black lead,Plin. 34, 17, 48, § 160.
* Subst.: tertĭārĭum, ii, n., a third part, a third, Cato, R. R. 95, 1; Vitr. 4, 7, 5.
Charlton T. Lewis, Charles Short, A Latin Dictionary