o

Noun

• the blood group whose red cells carry neither the A nor B antigens
  • people with type O blood are universal donors
    

• the 15th letter of the Roman alphabet

• 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

Related words

• Synonyms: 
  O , type O , group O , oxygen , atomic number 8