O - Definition
o
n 1: 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, O, atomic
number 8]
2: the 15th letter of the Roman alphabet [syn: O, o]
3: the blood group whose red cells carry neither the A nor B
antigens; "people with type O blood are universal donors"
[syn: O, type O, group O]