- (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.
"In the western world, women usually have long hair while men usually have short hair."
- (obsolete) Haircloth; a hair shirt.
- (countable) A pigmented filament of keratin which grows from a follicle on the skin of humans and other mammals.
- (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)."
- (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.
- (countable) Any very small distance, or degree; a hairbreadth.
"Just a little louder please—turn that knob a hair to the right."