If you realize the angry pit bull growling at you isn't on a leash after all, you're in peril. The word means imminent danger to life and limb.
Peril comes from the Latin peric(u)lum, meaning danger. Today it's often used in tandem with the word mortal, which relates to death. For example, you're in mortal peril when you're flying down a cliff-side trail on your mountain bike and you hit loose gravel. Peril can also describe dangers of a less physical sort, though it's less common. If your employer sunk your 401K into what turned out to be a Ponzi scheme, he's put your retirement in peril.