monstrĭfĭcus, a, um, adj. [monstrumfacio], monstrous, strange (post-Aug.): artes, i. e. magical, Val. Fl. 6, 152: natura hyaenae, Plin. 28, 8, 27, § 92: hominum ingenia, id. 21, 5, 13, § 26: effigies, id. 2, 3, 3, § 7; and so the better reading, Plin. 6, 30, 35, § 187; 36, 13, 19, § 88.
Hence, adv.: monstrĭfĭcē, in a monstrous or strange manner (post-Aug.), Plin. 28, 11, 49, § 181.