helmet

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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. n. The headgear with a glass mask worn by deep-sea divers.
3. n. A pith helmet; a topi.
4. n. A head covering, such as a balaclava, that is shaped like a helmet.
5. n. A piece of armor, usually made of metal, designed to protect the head.
6. n. Botany The hood-shaped sepal or corolla of some flowers.
7. v. To provide with or put on a helmet.

Century Dictionary and Cyclopedia

1. n. A defensive cover for the head. The term is applied in general to all defensive head-coverings except the slightest, such as the skull-cap, the secret, the wire hat, etc., and also the camail or coif. Specifically — Milit.: In ancient and medieval armor, a cap of metal worn to protect the head from sword-cuts and spear-thrusts. Such a helmet usually guarded the nape of the neck and sides of the face by means of hinged pieces or sliding splints (see coucre-nuque, face-guard, cheekpiece); and to a certain extent the face by means of a nasal, either fixed or movable, a beaver, a projecting vizor, or the like. The only helmets which covered the head and face completely were those worn by Roman gladiators of certain classes, and by medieval heavy-armed horsemen between the beginning of the thirteenth and the-middle of the sixteenth century; the most completely defensive helmets were the tilting-helmets of the fifteenth and sixteenth centuries, which prevented the wearer from seeing except directly before him, and at a height on a line with his eyes. See armet, barrel helm (under helm), basinet, beaver, burganet, cabasset, heaume, iron-cap, lumière, mentonnière, morion, nasal, œillère, ombril, tilting-helmet, vizor.
2. n. () In present use, a stiff military hat of domed or pointed form, sometimes of metal or stiffened with bars of metal so as to afford defense against a sword-cut.
3. n. A hat, usually of leather and having a vizor and broad neckguard, worn by firemen.
4. n. A hat of similar form worn by policemen, or by civilians for any purpose, especially in not climates. Such hats are usually of felt or pith, so formed as to have space for ventilation around the head or openings for ventilation above.
5. n. The headpiece of a suit of submarine armor. It is usually formed of sheetmetal and leather, and is fitted over the head and shoulders. It is provided with thick glass windows for the eyes and with pipes for air. See submarine, armor, under armor.
6. n. A havelock used by anglers, with a projection in front of the face that can be covered by a netting or veil as a protection against insects.
7. n. In heraldry, the representation of a helmet, set above the escutcheon and seeming to support the armorial crest. Distinctions of rank are indicated by the metal, the number of bars in the vizor, and the position.
8. n. Same as helm
9. n. In botany, same as galea, 1 .
10. n. The upper part of a retort.
11. n. In entomology, the galea of an insect's maxilla.
12. n. plural A breed of small, fancy pigeons which have a white body and the tail and top of head black or red. The name is given in allusion to this cap or helmet.

Wiktionary

1. n. A protective head covering.

GNU Webster's 1913

1. n. (Armor) A defensive covering for the head. See casque, headpiece, morion, sallet, and Illust. of beaver.
2. n. (Her.) The representation of a helmet over shields or coats of arms, denoting gradations of rank by modifications of form.
3. n. A helmet-shaped hat, made of cork, felt, metal, or other suitable material, worn as part of the uniform of soldiers, firemen, etc., also worn in hot countries as a protection from the heat of the sun.
4. n. That which resembles a helmet in form, position, etc.
5. n. (Chem.) The upper part of a retort.
6. n. (Bot.) The hood-formed upper sepal or petal of some flowers, as of the monkshood or the snapdragon.
7. n. (Zoöl.) A naked shield or protuberance on the top or fore part of the head of a bird.

WordNet 3.0

1. n. a protective headgear made of hard material to resist blows
2. n. armor plate that protects the head