Something shaped like the letter O.
Orgasm.
The number of overs bowled.
American Library Association abbreviation of octavo, a book size (20-25 cm).
Someone associated with Leyton Orient Football Club, as a player, coach, supporter etc.
Opium.
A blood type that lacks A or B antigens and may only receive transfusions of similar type O blood, but may donate to all (neglecting Rh factor). Synonym: universal donor.
The English vocative particle, used for direct address.
A surname from Korean.
The fifteenth letter of the English alphabet, called o and written in the Latin script.
The 15th letter of the Classical and Modern Greek alphabets (16th in Ancient and Old Greek), used in ordering lists as in naming (astronomy) the 15th star of a constellation or (epidemiology) the 15th discovered major variant of a disease.