Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
horrĭpĭlo, āre, v. n. [horreo-pilus], to bristle with hairs, be shaggy (post-class.): aures immodicis horripilant auctibus, App. M. 3, p. 140: horripilo ὀρθοτριχάω, horripilatur ὀρθοτριχεῖ, Gloss. Philox.