Dangerous means likely to cause harm, injury, or damage. A dangerous situation is one where someone could get hurt: a frayed electrical cord is dangerous because it might spark a fire, and a rickety old ladder is dangerous because it could collapse. A dangerous animal, like a rattlesnake or grizzly bear, has the ability and sometimes the inclination to injure people.

The word describes both things and situations. A sharp knife is dangerous if handled carelessly, but safe in the hands of an experienced chef who respects its edge. A steep cliff becomes dangerous in fog when you can't see where the edge is. Fast-moving water, thin ice, and severe thunderstorms are all dangerous because they create conditions where accidents can easily happen.

People sometimes confuse dangerous with difficult or scary. Climbing a rock wall at the gym might feel scary, but it's not actually dangerous because you're wearing safety equipment and trained staff are watching. A truly dangerous activity is one where real harm could occur.