O (A.C. Acoustics album)
WordNet
noun
(1) The blood group whose red cells carry neither the A nor B antigens
"People with type O blood are universal donors"
(2) The 15th letter of the Roman alphabet
(3) 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