o' /ə, o/
  O'.  A prefix to Irish family names, which signifies grandson or descendant of, and is a character of dignity; as, O'Neil, O'Carrol.
  O' prep. A shortened form of of or on. “At the turning o' the tide.”
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  O
       n 1: the blood group whose red cells carry neither the A nor B
            antigens; "people with type O blood are universal
            donors" [syn: type O, group O]
       2: a nonmetallic bivalent element that is normally a colorless
          odorless tasteless nonflammable diatomic gas; constitutes
          21 percent of the atmosphere by volume; the most abundant
          element in the earth's crust [syn: oxygen, atomic
          number 8]
       3: the 15th letter of the Roman alphabet