letter O

O

1 the fifteenth letter of the alphabet, denoting the next after N in a set of items, categories, etc.
2. a human blood type (in the ABO system) lacking both the A and B antigens. In blood transfusion, a person with blood of this group is a potential universal donor.
3. zero (in a sequence of numerals, esp. when spoken).
4. a shape like that of a capital O; a circle.
5. archaic spelling of oh.