Definition of brain noun from the Oxford Advanced American Dictionary

      

    brain

     noun
    noun
    NAmE//breɪn//
     
     
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    in head
  1. 1[countable] the organ inside the head that controls movement, thought, memory, and feeling damage to the brain brain cells She died of a brain tumor. a device to measure brain activity during sleep
  2. food
  3. 2brains [plural] the brain of an animal, eaten as food sheep's brains
  4. intelligence
  5. 3 [uncountable, countable, usually plural] the ability to learn quickly and think about things in a logical, and intelligent way It doesn't take a lot of brains to figure out that both stories can't be true. Teachers spotted that he had a good brain at an early age. You need brains as well as brawn (= intelligence as well as strength) to do this job. see also no-brainer
  6. intelligent person
  7. 4[countable] (informal) an intelligent person one of the best scientific brains in the country
  8. 5the brains [singular] the most intelligent person in a particular group; the person who is responsible for thinking of and organizing something He's always been the brains of the family. The band's drummer is the brains behind their latest venture.
  9. Idioms
    beat your brains out(informal)
     
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    to think very hard about something for a long time I've been beating my brains out all weekend to get this script written.
    blow your/somebody's brains out(informal)
     
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    to kill yourself/someone by shooting yourself/them in the head
    have something on the brain(informal)
     
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    to think about something all the time, especially in a way that is annoying He has football on the brain.
    pick somebody's brains(informal)
     
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    to ask someone a lot of questions about something because they know more about the subject than you do
    rack your brain(s)
     
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    to think very hard or for a long time about something She racked her brains, trying to remember exactly what she had said.
See the Oxford Advanced Learner's Dictionary entry: brain