Skully, “toboggan,” and “ski cap” are all names for a watch cap, a close-fitting knitted hat designed to keep the head warm. The style is usually made from wool, acrylic, or another insulating fabric and is commonly worn in cold weather.
The name “watch cap” comes from maritime tradition. Sailors and other people standing watch outdoors used compact knitted caps to protect themselves from cold and wind. The hat’s snug shape was practical: it stayed on the head, fit beneath other equipment, and did not have a brim that could obstruct vision.
Regional vocabulary varies widely. In parts of the United States, especially the South, “toboggan” can mean a knitted winter hat rather than a sled. “Skully” and “ski cap” are also informal names for closely related beanies. A watch cap is therefore not a special piece of ski equipment; it is a general cold-weather knit cap, often with a folded cuff around the ears.