fascinator
A light, decorative headpiece consisting of feathers, flowers, beads, netting, etc. attached to a comb or hair clip worn by women. They may be worn standalone or paired with a hat, such as a pillbox hat or sun hat.
In contrast to a hat, it is purely ornamental: it covers very little of the head and offers little or no protection from the weather.
This also includes cocktail hats, a nearly similar headpiece with mainly technical differences dividing them from fascinators.