frightful (adj.)
- abhorrent
- abominable
- alarming
- appalling
- atrocious
- awful
- awing
- chilling
- daunting
- deadly
- deterrent
- disagreeable
- disconcerting
- discouraging
- disheartening
- dismaying
- disquieting
- dreadful
- fearful
- fearsome
- forbidding
- formidable
- foul
- frightening
- ghastly
- grisly
- gruesome
- hideous
- horrendous
- horrible
- horrid
- horrific
- horrifying
- howling
- loathsome
- lurid
- macabre
- nasty
- nauseating
- nauseous
- offensive
- repelling
- repugnant
- repulsive
- revolting
- rousing
- scary
- shocking
- startling
- terrible
- terrific
- thumping
- ugly
- unspeakable
- vile
- whacking
Like one that on a lonesome road
Doth walk in fear and dread,
And having once turned round walks on,
And turns no more his head,
Because he knows a frightful fiend
Doth close behind him tread.