Lewis & Short

trĭĕtērĭcus, a, um, adj., = τριετηρικός, recurring every three years, triennial: sacra, the festival of Bacchus, Ov. M. 6, 587; also called trieterica orgia, Verg. A. 4, 302.
As subst.: trĭĕtērĭca, ōrum, n., the festival of Bacchus, Ov. R. Am. 593; Stat. Th. 2, 661; id. Achill. 1, 595; Hyg. Fab. 131; cf. trieteris.