O
— Noun
– English
~ the blood group whose red cells carry neither the A nor B antigens; "people with type O blood are universal donors"
O
— Noun
– English
~ 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
O. Henry
— Noun
– English
~ United States writer of short stories whose pen name was O. Henry (1862-1910)
O level
— Noun
– English
~ the basic level of a subject taken in school
O
— Noun
– English
~ the 15th letter of the Roman alphabet