adjective

unfriendly or threatening in appearance.

a grim and forbidding building

hostile,unwelcoming,unfriendly,unsympathetic,unapproachable,harsh,grim,stern,hard,tough,cool,cold,chilly,frosty,disagreeable,nasty,mean,abhorrent,repellent,off-putting,threatening,ominous,menacing,sinister,brooding,daunting,fearsome,frightening,chilling,disturbing,disquieting,uninviting,mean-looking,foreboding,unpromising,inauspicious,evil-looking,suggestive of evil,spooky,scary,creepy,direful,bodeful