Lewis & Short

caustĭcus, a, um, adj., = καυστικός, burning, caustic, corrosive: natura, Plin. 27, 9, 54, § 77: vis, id. 32, 10, 52, § 140: spuma, a kind of soap with which the Germans colored their hair, Mart. 14, 26, 1.
Subst.: caustĭcum, i, n. (sc. medicamentum), a burning, corroding medicament, Plin. 26, 1, 3, § 3; 26, 8, 39, § 65; 34, 18, 56, § 178.