Definition of common adjective from the Oxford Advanced American Dictionary

      

    common

     adjective
    adjective
    NAmE//ˈkɑmən//
     
    (commoner, commonest)
     
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  1. 1 more common and most common are more frequent happening often; existing in large numbers or in many places Jackson is a common American name. Breast cancer is the most common form of cancer among women in this country. Some birds which were once a common sight are now becoming rare. a common spelling mistake Allergies to milk are quite common in childhood. opposite uncommon
  2. 2 [usually before noun] common (to somebody/something) shared by or belonging to two or more people or by the people in a group They share a common interest in photography. basic features which are common to all human languages We are working together for a common purpose. common ownership of the land This decision was made for the common good (= the advantage of everyone). It is,by common consent, Oregon's prettiest bay (= everyone agrees that it is).
  3. 3[only before noun] ordinary; not unusual or special the common garden frog Shakespeare's work was popular among the common people in his day. In most people's eyes she was nothing more than a common criminal. You'd think he'd have the common courtesy to apologize (= this would be the polite behavior that people would expect). It's only common decency to let her know what's happening (= people would expect it).
  4. Idioms
    be common/public knowledge
     
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    to be something that everyone knows, especially in a particular community or group Their relationship is common knowledge.
    the common touch
     
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    the ability of a powerful or famous person to talk to and understand ordinary people
    make common cause with somebody(formal)
     
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    to be united with someone about something that you both agree on, believe in, or wish to achieve
See the Oxford Advanced Learner's Dictionary entry: common