also: めんぼお
noun
A protective face covering, especially the metal mask or visor attached to a samurai helmet (kabuto). Historical term.
甲冑の面頬は、顔を守るだけでなく、威嚇の意味もあった。
The face guard of the armor not only protected the face but also served to intimidate.
Compound of 面 (men, 'face') and 頬 (hō, 'cheek'), referring to a face-and-cheek guard. The reading めんぽお is a regular on'yomi combination; めんぼお is a variant with rendaku-like voicing.