Definition of brother noun from the Oxford Advanced American Dictionary

      

    brother

     noun
    noun
    NAmE//ˈbrʌðər//
     
     
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    in family
  1. 1a boy or man who has the same mother and father as another person We're brothers. He's my brother. an older/younger brother a twin brother Does she have any brothers and sisters? Edward was the youngest of the Kennedy brothers. He was like a brother to me (= very close). see also half-brother, stepbrother
  2. in religious group
  3. 2 Brother (pl. brethren or brothers) a male member of a religious group, especially a monk Brother Luke The Brethren meet regularly for prayer.
  4. at college
  5. 3 a member of a fraternity (= a club for a group of male students at a college)
  6. form of address
  7. 4 (informal) used by black people as a form of address for a black man
  8. other men
  9. 5 (brothers or (old-fashioned)brethren) used for talking to or talking about other male members of an organization or other men who have the same ideas, purpose, etc. as yourself We must work together, brothers! We are all brothers in the fight against injustice. He was greatly respected by his brother officers. We must support our weaker brethren.
See the Oxford Advanced Learner's Dictionary entry: brother