1. A head covering of hard material, such as leather, metal, or plastic, worn by football players, firefighters, construction workers, motorcyclists, and others to protect the head. 2. The headgear with a glass mask worn by deep-sea divers. 3. A pith helmet; a topi. 4. A head covering, such as a balaclava, that is shaped like a helmet. 5. A piece of armor, usually made of metal, designed to protect the head. 6. The hood-shaped sepal or corolla of some flowers. 7. To provide with or put on a helmet.
