Trias \Tri"as\, n. [L., triad. See Triad.]

(Geol.) The formation situated between the Permian and Lias, and so named by the Germans, because consisting of three series of strata, which are called in German the Bunter sandstein, Muschelkalk, and Keuper.

Source: Webster's Revised Unabridged Dictionary (1913)