(botany, countable) A cellular outgrowth of the epidermis, consisting of one or of several cells, whether pointed, hooked, knobbed, or stellated.
(countable) A pigmented filament of keratin which grows from a follicle on the skin of humans and other mammals.
(countable) Any slender, flexible outgrowth, filament, or fiber growing or projecting from the surface of an object or organism.
(countable) Any very small distance, or degree; a hairbreadth.
(countable, engineering, firearms) A locking spring or other safety device in the lock of a rifle, etc., capable of being released by a slight pressure on a hair-trigger.
(obsolete) Haircloth; a hair shirt.
(slang, uncountable) Complexity; difficulty; the quality of being hairy.
(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.
(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.
verb
(intransitive) To grow hair (where there was a bald spot).
(transitive) To cause to have or bear hair; to provide with hair
