The Collaborative International Dictionary of English v.0.48:
Aventail \Av"en*tail\, n. [OF. esventail. Cf. Ventail.] The movable front to a helmet; the ventail. [1913 Webster]WordNet (r) 3.0 (2006):
aventail n 1: a medieval hood of mail suspended from a basinet to protect the head and neck [syn: camail, aventail, ventail]