when doubled, woolen ball on a hat

The term for a woolen ball on a hat is a "pompon" or "pom-pom." When doubled, it is called a "pom pom." This decorative ball is typically found on woolen hats like beanies or bobble hats. Historically, pom-poms have served both a decorative and practical purpose. They were used by various military regiments to denote rank or regiment and were also worn by sailors to cushion their heads from low ship ceilings. The pom-pom helped cover seams or holes at the top of knitted or fabric hats. The word "pom-pom" comes from the French word "pompon," meaning a bobble or small ball of fabric. Pom-poms date back to at least Viking times in Scandinavia and have been part of traditional clothing across different cultures, including Scottish Highland regiments and Roman Catholic clergy, where the color of the pom-pom indicated rank. Nowadays, pom- poms are mainly a fashion accessory on winter hats.