o

noun pl. O's, o's

1. the fifteenth letter of the English alphabet: from the Greek omega and omicron, both borrowed from the Phoenician
2. any of the speech sounds that this letter represents, as, in English, the vowel (ō) of boat, (ä) of hot, or (ô) of wrong
3. a type or impression for o or O
4. the fifteenth in a sequence or group
5. an object shaped like

adjective

1. of o or O
2. fifteenth in a sequence or group
3. shaped like ; circular or oval in shape

1. octavo
2. old
3. only

noun pl. O's

1. popularly the figure zero; nought: in printed matter, zero is usually differentiated from the letter O, as in this dictionary: “O” is the character used for the letter, “0” is the character used for the number
2. a blood type

interjection

1. used in direct address: O Lord!
2. used to express surprise, wonder, fear, pain, etc.: now usually oh
3. used at the end of a line in some ballads

noun pl. O's

1. Ocean
2. October
3. Ohio
4. Physics ohm
5. Linguis. Old: OFr
6. Ontario
7. Baseball out(s)
8. Pharmacy pint