Definition of horn noun from the Oxford Advanced Learner's Dictionary

  1. 1   [countable] a hard pointed part that grows, usually in pairs, on the heads of some animals, such as sheep and cows. Horns are often curved. See related entries: Farm animals, Parts of animals
  2. 2[uncountable] the hard substance of which animal horns are made
  3. 3  [countable] a simple musical instrument that consists of a curved metal tube that you blow into a hunting horn See related entries: Musical instruments
  4. 4[countable] (especially British English) = French horn a horn concerto
  5. 5  [countable] a device in a vehicle for making a loud sound as a warning or signal to honk your car horn (British English) to sound/toot your horn Behind him, a horn blared. see also foghorn See related entries: Parts of a car, Motoring problems and accidents
  6. Word OriginOld English, of Germanic origin; related to Dutch hoorn and German Horn, from an Indo-European root shared by Latin cornu and Greek keras.Extra examples He gave a furious blast on his horn. Impatient horn blasts began to sound behind him. Passing motorists honked their horns. a large bull with curved horns ornaments made of rhino horn She flashed her lights and honked her horn at the car in front.Idioms
    blow/toot your own horn
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    (North American English, informal) = blow your own trumpet
    draw/pull your horns in
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    to start being more careful in your behaviour, especially by spending less money than before Small businesses have had to pull their horns in during the recession.
    lock horns (with somebody) (over something)
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    to get involved in an argument or a disagreement with somebody The company has locked horns with the unions over proposed pay cuts.
    on the horns of a dilemma
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    in a situation in which you have to make a choice between things that are equally unpleasant The medical profession’s eagerness for scientific advance had impaled it on the horns of a dilemma, forcing an unnatural choice between science and morality.
    take the bull by the horns
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    to face a difficult or dangerous situation directly and with courage Nora decided to take the bull by the horns and organize things for herself.
See the Oxford Advanced American Dictionary entry: horn