Helpmore common and most common are more frequent1 happening often; existing in large numbers or in many placesJackson is a common English 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 mistakeAllergies to milk are quite common in childhood.
Oppositeuncommon2 [usually before noun] common (to somebody/something) shared by or belonging to two or more people or by the people in a groupThey share a common interest in photography.basic features which are common to all human languagesWe are working together for a common purpose.common ownership of the landThis decision was taken for the common good (= the advantage of everyone).It is, by common consent, Scotland's prettiest coast (= everyone agrees that it is).3 [only before noun] ordinary; not unusual or specialthe common garden frogShakespeare'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 behaviour that people would expect).It's only common decency to let her know what's happening (= people would expect it).4 (British English, disapproving) typical of somebody from a low social class and not having good mannersShe thought he was very common and uneducated.
common or garden(British English) (North American English garden-variety) (informal) ordinary; with no special features
the common touch
the ability of a powerful or famous person to talk to and understand ordinary people
more at be common/public knowledge at knowledge