A visor can be pictured as one stiff piece that sits in front of your face or just above your eyes, and stops something from reaching them. On a helmet it stops blows, wind and rain; on a cap, a car roof or a headband it stops sunlight; on an old mask it stops other people's looks. The piece is always flat or gently curved, always out in front, and usually it can be moved — lifted, pulled down, or turned aside — because you only want it there some of the time.
The word came into English from French: Middle English viser, from Anglo-Norman viser and Old French visiere. Its earliest English use is the face-piece of a helmet, which is also the most concrete picture the later uses hang on.
這個字從法文進入英文：中古英文 viser，來自 Anglo-Norman 的 viser 與古法文 visiere。英文裡最早的用法就是頭盔上那片擋臉的板子。後來的各種意思，可以想成都是從這片板子延伸出去的。
Wiktionary entry supplied in this packet (source_ref kaikki:3f6f69a190036ae4:577222460), etymology_text: "From Middle English viser, from Anglo-Norman viser and Old French visiere."
From the picture
擋在眼睛上方的那一片
同樣是一片伸在前面的板子，只是位置從整張臉往上移到眉毛上方，擋的東西也從碰撞換成太陽。只要看到「一片硬硬的東西橫在眼睛前面」，英文就可能叫它 visor。
noun · B1
The stiff curved part at the front of a cap that sticks out above your eyes and keeps sun or rain off your face. The source marks this use as American English.
帽簷
noun · B2
The part of a helmet that covers your face and can be lifted up or pulled down. It usually has a clear window, or narrow openings, so you can still see out while your face stays covered.
面罩／鏡片
noun · C1
A mask worn over the face so that people cannot tell who you are. This meaning is old: you meet it in old plays and old writing, not in everyday English today.
面具（古語）