An indication of impending danger or harm
Nightmares: Nightmares are the result of suppressing fear or they can contain a forewarning about something that is to come.
Blood types cannot be changed, but adequate forewarning allows precautions and treatments that limit the danger to unborn babies.
forewarning of the doubts and problems which may arise later.
forewarning students planning to study abroad in 2004/05 that this change might be introduced immediately.
forewarning the shipping company P&O of impending disaster.