ventail

noun3

1. •
   (historical) The movable front part of a medieval helmet, originally including the visor but later specifically the separate lower section.

   • A comely knight, all arm'd in complete wize, / Through whose bright ventayle lifted vp on hye / His manly face [...] Lookt foorth [...]. — 1590
2. •
   (historical) Synonym of aventail (“mail curtain or flap, on a helmet or a mail coif, that protects the lower face and neck”).

   • The Lednickie example has its nasal terminating in a small hook; this was almost certainly to support the mail ventail of the mail coif, and thus to provide better facial protection. — 2012
3. •
   (rare, historical) A vent or breathing-hole in a medieval helmet, for the admission of air.

   • 398. ventayles : a pun on ventails, 'something acting as a sail or fan', and ventails, the air holes or vents in the vizor of a helmet. — 1969