helmet dome; bowl of a helmet
Refers to the rounded top part of a traditional Japanese helmet (kabuto). Domain-specific military/historical term.
The helmet bowl is an important part that protects the head in armor.
protective iron plate on a headband
A metal plate worn on the forehead, attached to a cloth headband (hachimaki), used by lower-ranking warriors or as supplementary protection. Also a domain-specific historical term.
Ashigaru soldiers fought with a protective iron plate attached to their headbands.
Compound of 鉢 (hachi, 'bowl') and 金 (kane, 'metal'), with rendaku voicing. The exact historical derivation is uncertain, but the word describes metal bowl-shaped or plate-like head protection.