When someone looks at you menacingly, or speaks menacingly, they do it in a way that makes you expect something bad. You feel they might hurt you, shout at you, or make trouble. It is stronger than unfriendly: unfriendly can be only cold, but menacingly has a threat in it. Animals can move this way too — a dog that comes toward you slowly, making a low sound. You meet the word more in stories and news than in ordinary talk; a child would more often say in a scary way. Though actually, adults use it when they want the threat to be clear, not only the fear.