What does "eboshi", a traditional Japanese headdress, mean in Japanese?

Eboshi refers to a class of Japanese hats seen from at least the Nara period (covers the years from AD 710 to 794). They are uniformally of black cloth, usually hemp or similar, and later versions even used paper. The black color gave them their name, the Chinese characters translating to “bird hat” because it resembled the feathers of a black bird.

Originally they were soft and pliable, going around the head and covering the hair, while often falling back, a style which remained common with commoners and was known as 'nae-eboshi' (pliable eboshi). Eventually, the fabric was starched and lacquered, such that it took on a tall, upright shape. The shape varied with the rank and position of the wearer.

In modern times, the type of eboshi, completely covers the head which is fixed at the chin with the kakeo strap is used often, because the mage (chignon) to fix the eboshi has been abolished. We can see it worn by a gyoji (referee) of the grand sumo tournament.