impervĭus — Lewis & Short
impervĭus (inp-), a, um, adj.2. inpervius,
inaccessus, invius): amnis,Ov. M. 9, 106:
iter,Quint. 12, 11, 11; cf.
itinera (with interrupta),Tac. A. 3, 31:
tellus,inaccessible, Val. Fl. 2, 643.— Transf.:
lapis ignibus,Tac. A. 15, 43.