Sweater/ˈswetər/ Definition 1 of 2Pro Tip 1/3Seasonal Wear Sweaters are often worn in fall and winter to stay warm. As autumn arrives, I start wearing my favorite sweaters. Pro Tip 2/3Layering Clothes Sweaters can be layered over shirts or under jackets for extra warmth. He layered a button-up shirt under his knit sweater. Pro Tip 3/3Casual Attire Sweaters are usually casual but can be dressed up for semi-formal events. She paired her black sweater with a skirt for the office event.