morion
noun
°A kind of open helmet used in the 16th and 17th centuries, having no visor or bever, and somewhat resembling a hat.
"1786: The morion is a kind of open helmet, without visor or bever, somewhat resembling a hat; it was commonly worn by the harqubussiers and musqueteers. — Francis Grose, A Treatise on Ancient Armour and Weapons, page 12."