If someone does something menacingly, they do it in a way that makes others feel like they are in danger or scared.
The word menacingly makes people think of fear, danger, and feeling unsafe.
Examples:
He looked at me menacingly.
The dog growled menacingly.
She spoke menacingly to the other kids.
The cat stared at the mouse menacingly.
The dark figure approached menacingly.
The villain laughed menacingly as he tied up the hero.