The Collaborative International Dictionary of English v.0.48:

Casque \Casque\ (k[.a]sk), n. [F. casque, fr. Sp. casco See
   Cask.]
   A piece of defensive or ornamental armor (with or without a
   vizor) for the head and neck; a helmet.
   [1913 Webster]

         His casque overshadowed with brilliant plumes.
                                                  --Prescott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

casque
    n 1: (15-16th century) any armor for the head; usually ornate
         without a visor