Letter O & o

1. the fifteenth letter of the alphabet.
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. symbol, the chemical element oxygen.
6. archaic used before a name in direct address, as in prayers and poetry: give peace in our time, O Lord.
7. in prescriptions, it means a pint. (from Latin octarius )