1 frightful, repulsive, or revolting, to the senses or the mind (a hideous monster; a hideous pattern).
2 colloq. unpleasant.
Derivatives:
hideously adv. hideousness n.
Etymology: ME hidous f. AF hidous, OF hidos, -eus, f. OF hide, hisde fear, of unkn. orig.
Useful english dictionary. 2012.