late 14c., from O.Fr. horreur, from L. horror "bristling, roughness, rudeness, shaking, trembling," from horrere "to bristle with fear, shudder," from PIE base *ghers- "to bristle" (cf. Skt. harsate "bristles," Avestan zarshayamna- "ruffling one's feathers," L. eris (gen.) "hedgehog," Welsh garw "rough"). As a genre in film, 1936. Chamber of horrors originally (1849) was a gallery of notorious criminals in Madame Tussaud's wax exhibition.