ven·tail /ˈvɛnˌtel/
  Vent·ail n.  That part of a helmet which is intended for the admission of air, -- sometimes in the visor.
  Her ventail up so high that he descried
  Her goodly visage and her beauty's pride.   --Fairfax.
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  ventail
       n : a medieval hood of mail suspended from a basinet to protect
           the head and neck [syn: camail, aventail]