chapel de fer

[sha-pel duh fair]

noun, plural cha·pels de fer.

a medieval open helmet, often having a broad brim for deflecting blows from above.

Origin of chapel de fer

1895–1900; < Old French: hat of iron; see chapeau, ferrous

Also called war hat, kettle hat.

Of the smaller casque—helmet, or chapel-de-fer—we have already observed that some were worn beneath the coif-de-mailles.
Ancient Armour and Weapons in Europe
John Hewitt
Frequently a metal breastplate or plastron-de-fer, and a steel cap or chapel-de-fer, were worn under the mail.
A Handbook of Pictorial History
Henry W. Donald