casque

Etymology

Borrowed from French casque. Doublet of casco and cask.

noun

1. A helmet.
   He beheld his child dashed to pieces, and almost buried under an enormous helmet, an hundred times more large than any casque ever made for human being, and shaded with a proportionable quantity of black feathers. 1764, Horace Walpole, The Castle of Otranto, section I
2. A hard structure on the head of some birds, such as the hornbill or cassowary.
   Helmeted Hornbill, Rhinoplax vigil (CR): Restricted to the Thai-Malay Peninsula, Sumatra and Borneo, this is the only hornbill species whose casque is solid keratin and therefore carvable. 2015, James Eaton et al., “Trade-driven extinctions and near-extinctions of avian taxa in Sundaic Indonesia”, in Forktail, page 2, column 2