hid·e·ous (h?d??-?s)adj.1. Repulsive, especially to the sight; revolting. See Synonyms at ugly.2. Morally offensive; detestable: hideous acts of torture.3. Causing great harm or fear; terrible: a hideous disease.[Middle English, variant of hidous, from Anglo-Norman and Old French hideus, hisdeus, probably from Old French hisde, hide, horror, fright (probably from alteration, with expressive initial h, of Frankish *egisida, fright, from Germanic *agis?n, from *agiz, fear), or perhaps from Vulgar Latin *hispid?sus, horripilating (from Latin hispidus, rough, shaggy, bristly; probably akin to hirs?tus, hairy, hirsute).]hid?e·os?i·ty (-?s??-t?) n.hid?e·ous·ly adv.hid?e·ous·ness n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.