hair

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of the cylindrical, keratinized, often pigmented filaments characteristically growing from the epidermis of a mammal.
2. n. A growth of such filaments, as that forming the coat of an animal or covering the scalp of a human.
3. n. A filamentous projection or bristle similar to a hair, such as a seta of an arthropod or an epidermal process of a plant.
4. n. Fabric made from the hair of certain animals: a coat of alpaca hair.
5. n. A minute distance or narrow margin: won by a hair.
6. n. A precise or exact degree: calibrated to a hair.

Century Dictionary and Cyclopedia

1. n. One of the numerous fine filaments which more or less completely cover the skin of most mammals, and constitute the characteristic coat of this class of animals; any capillary outgrowth from the skin. Hairs are extravascular, non-nervous, epidermal, or exoskeletal structures belonging to the same category as nails scales, feathers, and other horny or cuticular outgrowths, being chiefly distinguished by their simplicity, and their extreme slenderness in proportion to their length, which may reach several feet. A hair consists of an outer or cuticular layer of cells, extremely variable in the details of their arrangement, generally imbricated and with their free edges presenting away from the skin. These constitute the hair-cuticle or cortex, upon the nature of which largely depends the capability of being woven or felted of some kinds of hair, as wool. Inside the cuticle is a tubular shaft of longitudinal fibers, resulting from fibrillation of cells, which may contain a core of granular cells, the pith or medulla of the hair. Air finds its way into the interstices of the pith. Many hairs are quite cylindrical, or have but slightly reniform cross-section; such are apt to be long, slender, and straight, and possess the least felting properties, especially if their cuticular cells be also smooth. Curly, kinky, or woolly hairs, as of the negro's head or a man's beard, owe this character chiefly to the fact that they are flattened in different planes in successive parts of their length. Hairs of extreme length and fineness grow upon the head of women; others are of microscopic size, retaining, however, the same structural character. Hairs of great comparative thickness and stiffness are called bristles, as those on the back of swine, the whiskers of a cat, etc. When still stouter and sharppointed, bristles become spines, as of the hedgehog; one extremely short, broad, blunt, flattened spine becomes a scale, as on a pangolin; and a hair which tends to branch out iu a certain manner becomes a feather. (See feather.) An ordinary hair is divided into the root, which is inserted into the skin; the stem or shaft; and the point, which is the part into which the pith does not extend. The root is planted in a little pit or follicle formed by an inversion of the skin, the hair-follicle; this follicle has a dermic and an epidermic layer, and some of the latter which adheres when a hair is plucked out by the root is called the root-sheath. The root is commonly enlarged or bulbous, constituting the hair-bulb. Associated with the hair-follicle may be one or more sebaceous glands whose secretion keeps the hair glossy, and tiny muscles (arrectores pili) are sometimes attached to the sheath of the root, whose action may cause the hair to bristle or “stand on end.” (See horripilation.) Hair is sometimes colorless, but oftenest heavily pigmented, giving animals their natural colors, in which various shades of black, brown, and gray, with flaxen or yellow, are the commonest, the purer reds, blues, and greens being comparatively rare. In all species of mammals, including man, the hair attains a definite length on certain areas of the body; if cut off, it grows again. Most mammals have at least two sets of hairs: one comparatively long, stout, and straight, coming to the surface and overlying a finer shorter, and more curly set, among the roots of which latter a still finer coating of hairs may be found. The aggregate of the hairs is the pelage, corresponding to the Plumage of a bird; a copious pelage of fine hairs is a fur, as of the fur-seal, otter, beaver, etc.; the fur peculiar to animals of the sheep kind is called a fleece. In most animals the hairs have a definite period of growth, maturity, and decay, which results in the periodical shedding of the coat. Hair is a specially cuticular structure, and hence mostly confined to the exterior of the body; but since epidermis becomes insensibly modified into the epithelium of mucous membrane, so hairs may be found growing inside any of the natural openings of the body, as the ears, nostrils, mouth, and various cutaneous pouches of different animals. Like other horny structures, hairs are often a secondary sexual character, either appearing on certain parts of the body coincidently with the maturity of the sexual function (see puberty), or growing in a certain way in one sex and not in the other, as the human beard, the mane of the lion, etc. Though hairs are in themselves non-nervous, certain hairs on some animals constitute feelers or tactile organs of great delicacy; such are known as tactile hairs.
2. n. The aggregate of the hairs which grow on any mammal; hairs collectively or in the mass; in the widest sense, a dermal coat or covering either of hair (specifically so called), wool, or fur; pelage; in common use, the natural capillary covering of a person's head: formerly sometimes in the plural.
3. n. On animals, with the exception of most mammals, a filament; any fine capillary or hair-like outgrowth from the body or any part of it, but especially its surface; one of the objects which compose the hairiness, pubescence, or pilosity of an animal, or such objects collectively: used in both the singular and the plural: as, the hair or hairs of a caterpillar, that which clothes or those which clothe a lobster's gills, etc. Most members of the animal kingdom have hair or hairs of some kind, resembling the peculiar covering of mammals more or less nearly in appearance or function, or both, and consequently taking the same name, though the structural character of these appendages may be entirely different.
4. n. In botany, an expansion of the epidermis, consisting of a single cell or of a row or number of cells. Hairs assume a variety of forms, even the simple or unicellular ones being often branched, variously curved, or stellate. Cotton-fibers are hairs consisting of elongated single cells. Compound hairs may start from a single cell or a group of cells, and may have their derivative cells arranged in many ways. According to form, hairs may be called capitate, clavate, uncinate, barbed, peltate, etc. They are often glandular and viscid at the extremity. Most hairs or branches of hairs in plants are more or less conical.
5. n. Haircloth; a garment of haircloth, especially a hair shirt used for penance.
6. n. A cloth, mat, or other fabric of hair used for various purposes in the trades, as in the extraction of oils, manufacture of soap from cocoanut-oil, etc.
7. n. Particular natural set or direction; course; order; drift; grain; character; quality.
8. n. In mech., a locking spring or other safety contrivance in the lock of a rifle or pistol, which may be released by a very slight pressure on a hair-trigger.
9. n. One of the polyps, as sertularians and others, which grow on oyster-shells. See graybeard, 3, and redbeard.
10. Made of or stuffed with hair: as, hair jewelry; a hair mattress.
11. To produce or grow hair.
12. Another spelling of hare.
13. To form fine fibers, as syrup, when tested by dripping.

Wiktionary

1. n. countable A pigmented filament of keratin which grows from a follicle on the skin of humans and other mammals.
2. n. uncountable The collection or mass of such growths growing from the skin of humans and animals, and forming a covering for a part of the head or for any part or the whole body.
3. n. zoology, countable A slender outgrowth from the chitinous cuticle of insects, spiders, crustaceans, and other invertebrates. Such hairs are totally unlike those of vertebrates in structure, composition, and mode of growth.
4. n. botany, countable A cellular outgrowth of the epidermis, consisting of one or of several cells, whether pointed, hooked, knobbed, or stellated. Internal hairs occur in the flower stalk of the yellow frog lily (Nuphar).
5. n. obsolete Haircloth; a hair shirt.
6. n. countable Any very small distance, or degree; a hairbreadth.

GNU Webster's 1913

1. n. The collection or mass of filaments growing from the skin of an animal, and forming a covering for a part of the head or for any part or the whole of the body.
2. n. One the above-mentioned filaments, consisting, in vertebrate animals, of a long, tubular part which is free and flexible, and a bulbous root imbedded in the skin.
3. n. Hair (human or animal) used for various purposes.
4. n. (Zoöl.) A slender outgrowth from the chitinous cuticle of insects, spiders, crustaceans, and other invertebrates. Such hairs are totally unlike those of vertebrates in structure, composition, and mode of growth.
5. n. (Bot.) An outgrowth of the epidermis, consisting of one or of several cells, whether pointed, hooked, knobbed, or stellated. Internal hairs occur in the flower stalk of the yellow frog lily (Nuphar).
6. n. A spring device used in a hair-trigger firearm.
7. n. obsolete A haircloth.
8. n. Any very small distance, or degree; a hairbreadth.

WordNet 3.0

1. n. a very small distance or space
2. n. a filamentous projection or process on an organism
3. n. filamentous hairlike growth on a plant
4. n. any of the cylindrical filaments characteristically growing from the epidermis of a mammal
5. n. a covering for the body (or parts of it) consisting of a dense growth of threadlike structures (as on the human head); helps to prevent heat loss
6. n. cloth woven from horsehair or camelhair; used for upholstery or stiffening in garments