What is the meaning of Ventail?

Synonym of aventail (mail curtain or flap, on a helmet or a mail coif, that protects the lower face and neck)

The movable front part of a medieval helmet, originally including the visor but later specifically the separate lower section.

A vent or breathing-hole in a medieval helmet, for the admission of air.

post-1990 spelling of vantail

Source: wiktionary.org