Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
portentĭfĭcus, a, um, adj. [portentum-facio], marvellous, monstrous, unnatural, extraordinary (poet. and in post-class. prose): venena, Ov. M. 14, 55 Jahn (al. portentifera): figurae animalium, Lact. 2, 13, 11: opera, id. 4, 13, 15.