ominous
Definition of abbreviation (noun) -
delivering bad news; foreboding; threateningPart of speech:
AdjectiveThe sky looks very ominous before a tornado.
He was cutting his journey fine and it was only by actually jogging from Friedrichstrasse, and feeling a fool for doing so, apart from almost breaking his neck by slipping on the icy pavement, that he arrived at his office before the ominous red line was drawn.
Nowadays in Hungary, when the dismantling of red stars -- from public buildings, from railway engines, and perhaps even from the gravestones of party members --; has become a minor industry, nobody worries about ominous knocks on the door.
Seeing ominous clouds on the horizon, the street fair organizers decided to fold up their tent and go home.