1911 Encyclopædia Britannica/Beaver (armour)

BEAVER (from Fr. bavière, a child’s bib, from bave, saliva), the lower part of the helmet, fixed to the neck-armour to protect the face and cheeks; properly it moved upwards, as the visor moved down, but the word is sometimes used to include the visor. The right form of the word, “baver,” has been altered from a confusion with “beaver,” a hat made of beaver-fur or a silk imitation, also, in slang, called a “castor,” from the zoological name of the beaver family.