Baleful means the foreshadowing of tragic or evil events. If no one's listening in class and your teacher reprimands you with a baleful glance, expect a pop quiz.
If your car breaks down and you take refuge in a deserted mansion, you might huddle under a dusty blanket and find yourself thinking that the wind moaning at the windows sounds baleful — maybe it's really the voice of a young woman murdered in the very bed where you sleep?