1. (a.) Scary, alarming, appalling\.

2. (a.) Full of that which causes fright; exciting alarm; impressing terror; shocking; as, a frightful chasm, or tempest; a frightful appearance.

abhorrent abominable alarming appalling atrocious awful awing chilling daunting deadly deterrent deterring disagreeable disconcerting discouraging disheartening dismaying disquieting dreadful fear-inspiring fearful fearsome forbidding formidable foul frightening ghastly grisly gruesome hideous horrendous horrible horrid horrific horrifying howling loathsome lurid macabre nasty nauseating nauseous offensive overawing repelling repugnant repulsive revolting rousing scaring scary shocking startling terrible terrific thumping ugly unspeakable vile whacking