trīcennālis — Lewis & Short
trīcennālis, e, adj.tricennium,
I of or belonging to thirty years, tricennial (late Lat.):
incuria,Ruf. in Hier. 1, 11.—In plur. subst.: trīcennālia, ĭum, n., a festival celebrated once in thirty years, a tricennial festival, Oros. 7, 28 fin.