Meaning: This sentence describes the way the cold air in autumn can make your skin feel cold, especially at dusk.
Choice of Words: "Crisp" means firm and brittle, often used to describe the texture of food or air. "Air" is the mixture of gases that surrounds the Earth. "Chills" is a verb that means to make something feel cold. "Skin" is the outer covering of a person's or animal's body. "Dusk" is the time of day when the sun is setting.