Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
horrĭfer, ĕra, ĕrum (archaic gen. plur. horriferum, Pac. ap. Cic. Or. 46, 155), adj. [horror-fero], that brings trembling or terror, terrible, dreadful, horrible, horrific (poet.): unde horrifer Aquiloni’ stridor gelidas molitur nives, Att. ap. Cic. Tusc. 1, 28, 68: Boreas, Ov. M. 1, 65; 15, 471: axis, Val. Fl. 5, 518: nix, id. 5, 307: prodigium horriferum, Pac. ap. Cic. Or. 46, 155: aestus (Tartari), Lucr. 3, 1012: Aegis (= δεινή, Hom.), Verg. A. 8, 435: Erinys, Ov. M. 1, 725: voces, Lucr. 5, 996.