From Middle English hidous, from Anglo-Norman hidous, from Old French hideus, hydus (“that which inspires terror”), from earlier hisdos, from hisda (“horror, fear”), of uncertain and disputed origin. Probably from Frankish *egisda, *egisida (“terror, fright”), from Proto-Germanic *agisiþō (“horror, terror”), from Proto-Germanic *agisōną (“to frighten, terrorise”), from Proto-Germanic *agaz (“terror, fear”), from Proto-Indo-European *aǵʰ-, *agʰ- (“to frighten”). Cognate with Old High German egisa, egidī (“horror”), Old English egesa (“fear, dread”), Gothic 𐌰𐌲𐌹𐍃 (agis, “fear, terror”).
- Frightful; shocking; extremely ugly.
- A piteous and hideous spectacle." Thomas Babington Macaulay.
- Distressing or offensive to the ear; horrible.
- Hateful; shocking.
- Sure, you have some hideous matter to deliver. - William Shakespeare
Usage notes 
- Nouns to which "hideous" is often applied: monster, creature, man, face, thing, crime, form, death, aspect, spectacle, picture, roar, sound, manner, way, disease, mistake, shape, dress, fact, act, smile.