helmet

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A protective head covering made of hard material, such as leather, metal, or plastic.
• noun The headgear with a glass mask worn by deep-sea divers.
• noun A pith helmet; a topi.
• noun A head covering, such as a balaclava, that is shaped like a helmet.
• noun A piece of armor, usually made of metal, designed to protect the head.
• noun Botany The hood-shaped sepal or corolla of some flowers.
• transitive & intransitive verb To provide with or put on a helmet.

from The Century Dictionary.

• noun In entomology, the galea of an insect's maxilla.
• noun 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.
• noun A defensive cover for the head.
• noun () 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.
• noun A hat, usually of leather and having a vizor and broad neckguard, worn by firemen.
• noun 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.
• noun 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.
• noun 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.
• noun 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.
• noun Same as helm
• noun In botany, same as galea, 1 .
• noun The upper part of a retort.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Armor) A defensive covering for the head. See casque, headpiece, morion, sallet, and Illust. of beaver.
• noun (Her.) The representation of a helmet over shields or coats of arms, denoting gradations of rank by modifications of form.
• noun 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.
• noun That which resembles a helmet in form, position, etc.
• noun (Chem.) The upper part of a retort.
• noun (Bot.) The hood-formed upper sepal or petal of some flowers, as of the monkshood or the snapdragon.
• noun (Zoöl.) A naked shield or protuberance on the top or fore part of the head of a bird.
• noun (Zoöl.) a leaf-eating beetle of the family Chrysomelidæ, having a short, broad, and flattened body. Many species are known.
• noun (Zoöl.) one of many species of tropical marine univalve shells belonging to Cassis and allied genera. Many of them are large and handsome; several are used for cutting as cameos, and hence are called cameo shells. See King conch.
• noun (Zoöl.) an African wood shrike of the genus Prionodon, having a large crest.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A protective head covering.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a protective headgear made of hard material to resist blows
• noun armor plate that protects the head