hideux m (feminine singular hideuse, masculine plural hideux, feminine plural hideuses)
From Middle French hideux, from Old French hideus, hydus, hisdos (“that which inspires terror”), from hide, hede, hisda (“horror, fear”), 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 *ag(')h- (“to frighten”). Cognate with Old High German egisa, egidī (“horror”), Old English egesa (“fear, dread”), Gothic 𐌰𐌲𐌹𐍃 (agis, “fear, terror”).
Alternative etymology cites possbile derivation from Latin hispidosus (“rugged”), from hispidus (“rough, bristly”), yet the semantic evolution is more difficult to trace.