alarming
dire
direful
dread
dreadful
fearful
fearsome
forbidding
foreboding
formidable
frightening
hair-raising
horrendous
horrible
horrifying
intimidating
redoubtable
shocking
spine-chilling
terrible
terrifying
daunting
demoralizing
disconcerting
discouraging
dismaying
disquieting
distressing
disturbing
perturbing
startling
threatening
troubling
trying
unnerving
atrocious
awful
dreadful
frightful
ghastly
grisline
gruesome
hideous
horrid
monstrosity
repulsive