O
— Noun
– English
～ the blood group whose red cells carry neither the A nor B antigens; "people with type O blood are universal donors"
O
— Noun
– English
～ 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
O. Henry
— Noun
– English
～ United States writer of short stories whose pen name was O. Henry (1862-1910)
O level
— Noun
– English
～ the basic level of a subject taken in school
O
— Noun
– English
～ the 15th letter of the Roman alphabet
O'Brien
— Noun
– English
～ Irish writer (born in 1932)
O'Casey
— Noun
– English
～ Irish playwright (1880-1964)
o'clock
— Adverb
– English
～ according to the clock; "it's three o'clock in Tokyo now"
O'Connor
— Noun
– English
～ United States writer (1925-1964)
o'er
— Adverb
– English
～ throughout a period of time; "stay over the weekend"
O'Flaherty
— Noun
– English
～ Irish writer of short stories (1896-1984)
o'hara
— Noun
– English
～ United States writer (1905-1970)
o'keeffe
— Noun
– English
～ United States painter (1887-1986)
O'Neill
— Noun
– English
～ United States playwright (1888-1953)
o'toole
— Noun
– English
～ British actor (born in Ireland in 1932)
o.d.
— Verb
– English
～ dose too heavily; "The rock star overdosed and was found dead in his hotel room"
O.E.D.
— Noun
– English
～ an unabridged dictionary constructed on historical principles
o.k.
— Noun
– English
～ an endorsement; "they gave us the O.K. to go ahead"
O.K.
— Verb
– English
～ give sanction to; "I approve of his educational policies"
o.k.
— Adjective
– English
～ being satisfactory or in satisfactory condition; "an all-right movie"; "the passengers were shaken up but are all right"; "is everything all right?"; "everything's fine"; "things are okay"; "dinner and the movies had been fine"; "another minute I'd have been fine"