any of various forms of protective head covering worn by soldiers, firefighters, divers, cyclists, etc.

medieval armor for the head.

(in fencing, singlestick, etc.) a protective device for the head and face consisting of reinforced wire mesh.

anything resembling a helmet in form or position.

noun

armor , busby , crash helmet , hard hat , hat , head protector , kepi , safety helmet , shako , basinet , burgonet , casque , crest , galea , headpiece , heaume , morion , salade , sallet