hair n
1. dense growth of hairs covering the body or parts of it (as on the human head); helps prevent heat loss; "he combed his hair"
2. a very small distance or space; "they escaped by a hair's-breadth"; "they lost the election by a whisker" [syn: hair's-breadth, hairsbreadth, whisker]
3. filamentous hairlike growth on a plant; "peach fuzz" [syn: fuzz, tomentum]
4. any of the cylindrical filaments characteristically growing from the epidermis of a mammal; "there is a hair in my soup" [syn: pilus]
5. cloth woven from horsehair or camelhair; used for upholstery or stiffening in garments [syn: haircloth]
6. a filamentous projection or process on an organism

Hair \Hair\, n. [OE. her, heer, h[ae]r, AS. h[=ae]r; akin to OFries, h[=e]r, D. & G. haar, OHG. & Icel. h[=a]r, Dan. haar, Sw. h[*a]r; cf. Lith. kasa.]
1. 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. One the above-mentioned filaments, consisting, in invertebrate animals, of a long, tubular part which is free and flexible, and a bulbous root imbedded in the skin. Then read he me how Sampson lost his hairs. --Chaucer. And draweth new delights with hoary hairs. --Spenser.
3. Hair (human or animal) used for various purposes; as, hair for stuffing cushions.
4. (Zo["o]l.) 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. 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. A spring device used in a hair-trigger firearm.
7. A haircloth. [Obc.] --Chaucer.
8. Any very small distance, or degree; a hairbreadth. Note: Hairs is often used adjectively or in combination; as, hairbrush or hair brush, hair dye, hair oil, hairpin, hair powder, a brush, a dye, etc., for the hair. Against the hair, in a rough and disagreeable manner; against the grain. [Obs.] ``You go against the hair of your professions.'' --Shak.

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. The human body, apart from its glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types and hair care, but hair is also an important biomaterial primarily composed of protein, notably keratin.

Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class. Hair-like structures, called cilia, but which are not classified as hair, are visible in organs such as the nose and ear and these structures also occur in many other organs of mammals, other animals, and plants. Although non-mammals, especially insects, show filamentous outgrowths, these are not considered "hair" either, in the scientific sense. These so-called "hairs" (trichomes) also are found on plants. The projections on arthropods, such as insects and spiders, are classified as bristles, which are composed of a polysaccharide called chitin. There are varieties of cats, dogs, and mice bred to have little or no visible hair (fur). In some species, hair is absent at certain stages of life.

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