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: {O}, {type O}, {group O}]
2: a nonmetallic bivalent element that is normally a colorless
odorless tasteless nonflammable diatomic gas; constitutes
28 percent of the atmosphere by volume; the most abundant
element in the earth's crust [syn: {oxygen}, {O}, {atomic
number 8}]