c. 1300, "terrifying, horrible, dreadful," from Anglo-French hidous, Old French hideus, earlier hisdos "hideous, horrible, awful, frightening" (11c.; Modern French hideux), from hisda "horror, fear," perhaps of Germanic origin. The old guess that it comes from Vulgar Latin *hispidosus, from Latin hispidus "shaggy, bristly," "presents numerous difficulties" [OED] and seems now to be generally discredited. Meaning "repulsive" is late 14c.
<a href="https://www.etymonline.com/word/hideosity">Etymology of hideosity by etymonline</a>
Harper, D. (n.d.). Etymology of hideosity. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/hideosity