[ hair ]
See synonyms for hair on
  1. any of the numerous fine, usually cylindrical, keratinous filaments growing from the skin of humans and animals; a pilus.

  2. an aggregate of such filaments, as that covering the human head or forming the coat of most mammals.

  1. a similar fine, filamentous outgrowth from the body of insects, spiders, etc.

  2. Botany. a filamentous outgrowth of the epidermis.

  3. cloth made of hair from animals, as camel and alpaca.

  4. a very small amount, degree, measure, magnitude, etc.; a fraction, as of time or space: He lost the race by a hair.

Idioms about hair

  1. get in someone's hair, Slang. to annoy or bother someone: Their snobbishness gets in my hair.

  2. hair of the dog, Informal. a drink of liquor, supposed to relieve a hangover: Even a hair of the dog didn't help his aching head.: Also hair of the dog that bit one.

  1. let one's hair down, Informal.

    • to relax; behave informally: He finally let his hair down and actually cracked a joke.

    • to speak candidly or frankly; remove or reduce restraints: He let his hair down and told them about his anxieties.

  2. make one's hair stand on end, to strike or fill with horror; terrify: The tales of the jungle made our hair stand on end.

  3. split hairs, to make unnecessarily fine or petty distinctions: To argue about whether they arrived at two o'clock or at 2:01 is just splitting hairs.

  4. tear one's hair, to manifest extreme anxiety, grief, or anger: He's tearing his hair over the way he was treated by them.: Also tear one's hair out.

  5. to a hair, perfect to the smallest detail; exactly: The reproduction matched the original to a hair.

  6. without turning a hair, without showing the least excitement or emotion.: Also not turn a hair.

Origin of hair

First recorded before 900; Middle English heer, Old English hǣr (cognate with Dutch, German haar, Old Norse hār ), with vowel perhaps from Middle English haire “hair shirt,” from Old French, from Old High German hāria (cognate with Middle English here, Old English hǣre, Old Norse hǣra )

Other words from hair

  • hairlike, adjective
  • de·hair, verb (used with object)

Words that may be confused with hair

Words Nearby hair Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use hair in a sentence

British Dictionary definitions for hair


/ (hɛə) /

  1. any of the threadlike pigmented structures that grow from follicles beneath the skin of mammals and consist of layers of dead keratinized cells

  2. a growth of such structures, as on the human head or animal body, which helps prevent heat loss from the body

  1. botany any threadlike outgrowth from the epidermis, such as a root hair

    • a fabric or material made from the hair of some animals

    • (as modifier): a hair carpet; a hair shirt

  2. another word for hair's-breadth to lose by a hair

  3. get in someone's hair informal to annoy someone persistently

  4. hair of the dog or hair of the dog that bit one an alcoholic drink taken as an antidote to a hangover

  5. keep your hair on! British informal keep calm

  6. let one's hair down to behave without reserve

  7. not turn a hair to show no surprise, anger, fear, etc

  8. split hairs to make petty and unnecessary distinctions

Origin of hair

Old English hær; related to Old Norse hār, Old High German hār hair, Norwegian herren stiff, hard, Lettish sari bristles, Latin crescere to grow

Derived forms of hair

  • hairlike, adjective

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for hair


[ hâr ]

  1. One of the fine strands that grow from the skin of mammals, usually providing insulation against the cold. Modified hairs sometimes serve as protective defenses, as in the quills of a porcupine or hedgehog, or as tactile organs, as in the whiskers (called vibrissae) of many nocturnal mammals. Hair filaments are a modification of the epidermis of the skin and are composed primarily of keratin. Hair also contains melanin, which determines hair color.

  2. A slender growth resembling a mammalian hair, found on insects and other animals.

  1. A fine, threadlike growth from the epidermis of plants. See more at trichome.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Other Idioms and Phrases with hair


In addition to the idioms beginning with hair

  • hair of the dog that bit you
  • hair shirt

also see:

  • bad hair day
  • by a hair
  • by the short hairs
  • fair-haired boy
  • get gray hair from
  • hang by a thread (hair)
  • hide or hair
  • in someone's hair
  • let one's hair down
  • make one's hair stand on end
  • put lead in one's pencil (hair on one's chest)
  • split hairs
  • tear one's hair
  • turn a hair

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.