Fascinator

Catherine, Princess of Wales, then Duchess of Cambridge, wearing a red fascinator during her visit to Canada in 2011
Antoine Watteau: Studies of a woman wearing a cap (1717–1718)

A fascinator is a formal headpiece, a style of millinery. Since the 1990s, the term has referred to a type of formal headwear worn as an alternative to the hat; it is usually a large decorative design attached to a band or clip. In contrast to a hat, its function is purely ornamental: it covers very little of the head and offers little or no protection from the weather. An intermediate form, incorporating a more substantial base to resemble a hat, is sometimes called a hatinator.