Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
horrĭfĭcē, adv., v. horrificus fin.
horrĭfĭcus, a, um, adj. [horror-facio], that causes tremor or terror, terrible, dreadful, frightful, horrific (poet. and in postAug. prose): bustum, Lucr. 3, 906: letum, Verg. A. 12, 851: ruinae (Aetnae), id. ib. 3, 571: lapsu (Harpyiarum), id. ib. 3, 225: fulmen, Val. Fl. 2, 97: acta, id. 3, 423: caesaries, Luc. 2, 372: poena, Gell. 20, 1 fin.
Adv.: horrĭfĭcē, in a manner to cause dread, with affright: horrifice fertur divinae Matris imago, Lucr. 2, 609; 4, 36.