O, letter. The fifteenth letter of the basic modern Latin alphabet.

O, symbol. (IPA) close-mid back rounded vowel

O, letter. The fifteenth letter of the English alphabet, called o and written in the Latin script.

O, noun. The name of the Latin-script letter O/o.

O, noun. A zero (used in reading out numbers).

O, interjection. (archaic) (always capitalized in modern usage) The English vocative particle, used before a pronoun or the name of a person or persons to mark direct address.

O, interjection. Alternative form of oh

O, noun. (IRC) Operator

O, noun. Object, see SVO

O, adjective. Over

O, letter. The fifteenth letter of the basic modern Latin alphabet.

O, symbol. (element symbol) Symbol for oxygen.

O, symbol. (mathematics) big O: a class of functions asymptotically bounded from above by a specific function, up to a constant factor

O, symbol. (linear algebra) (group theory) orthogonal group

O, letter. The fifteenth letter of the English alphabet, called o and written in the Latin script.

O, noun. 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.

O, abbreviation. (cricket) The number of overs bowled.

O, abbreviation. (slang) Orgasm. (Often used in the phrase the big O.)

O, noun. (printing) American Library Association abbreviation of octavo, a book size (20-25 cm).

O, noun. (soccer) Someone associated with Leyton Orient Football Club, as a player, coach, supporter etc.

Ó, letter. The letter o with an acute accent.

º, symbol. The masculine ordinal indicator

Ở, letter. The letter o with a horn and a hook.

Ò, letter. The letter o with a grave accent.

Ō, letter. The letter o with a macron.

Õ, letter. The letter o with a tilde.

Õ, letter. The letter O with a tilde.

Ô, letter. The letter o with a circumflex.

Ö, letter. The letter o with a diaeresis above itself.

Ö, letter. The letter o with an umlaut above itself.

Ｏ, letter. The letter o in fullwidth.

Ｏ, letter. The letter O in fullwidth.

Ờ, letter. The letter O with a horn and a grave accent.

Ờ, letter. The letter o with a horn and a grave accent.

Ớ, letter. The letter O with a horn and an acute accent.

Ớ, letter. The letter o with a horn and an acute accent.

Ở, letter. The letter O with a horn and a hook.

Ỡ, letter. The letter O with a horn and a tilde.

Ỡ, letter. The letter o with a horn and a tilde.

Ợ, letter. The letter O with a horn and a dot below.

Ợ, letter. The letter o with a horn and a dot below.

Ȯ, letter. The letter O with a dot above.

Ȯ, letter. The letter o with a dot above.

Ọ, letter. The letter O with a dot below.

Ọ, letter. The letter o with a dot below.

Ò, letter. The letter O with a grave accent.

Ô, letter. The letter O with a circumflex.

Ŏ, letter. The lowercase letter o with a breve above.

Ŏ, letter. The uppercase letter O with a breve above.

Ǫ, letter. The letter o with an ogonek.

Ǫ, letter. O caudata, a letter used in Old Norse. (See Wikipedia.)

Ö, letter. The letter O with a diaeresis.

Ö, letter. The letter O with an umlaut.

ℴ, symbol. (chiefly mathematics) The lower-case letter o in a Gothic or Fraktur font

Ō, letter. The letter o with a macron.

Ȫ, letter. The letter o with a diaeresis and a macron above it.

Ȫ, letter. The letter O with a diaeresis and a macron above it.

Ỏ, letter. The letter O with a hook above it.

Ỏ, letter. The letter p with a hook above it.

Ó, letter. The letter O with an acute accent above it.

Ố, letter. The letter O with a circumflex and acute above it.

Ố, letter. The letter o with a circumflex and acute above it.

Ǒ, letter. The letter o with a háček above it.

Ṏ, letter. The letter o written with a tilde and a diaeresis.

Ṏ, letter. The letter O written with a tilde and a diaeresis.

Ǭ, letter. The letter O with an ogonek and a macron.

Ǭ, letter. The letter o with an ogonek and a macron.

Ō̂, letter. The letter o with a macron and circumflex, used in transliterating ῶ from the Greek alphabet.

Ō̂, letter. The letter O with a macron and circumflex, used in transliterating capitalized ῶ from the Greek alphabet.

Ṓ, letter. The letter o with a macron and accent, used in transliterating ώ from the Greek alphabet.

Ṓ, letter. The letter O with a macron and accent, used in transliterating Ώ from the Greek alphabet.

O CANADA, proper noun. The national anthem of Canada

O CAUDATA, noun. (rare) A form of the letter o modified by the addition of a diacritical “tail”: ⟨ǫ⟩, used in Old Norse.

O CLIP, noun. A kind of crimped hose clip over a barbed spigot, used with gas hoses in oxyfuel welding and cutting.

O FOR, preposition. (poetic) I wish that I had; may there be granted; elliptically expressing desire or prayer.

O LEVEL, noun. Alternative spelling of O-level

O MARK, noun. A circle, which serves as a checkmark in Japanese: ◯.

O MARKS, noun. Plural of O mark

O MY GOD, interjection. Alternative form of oh my God

O O, symbol. An emoticon representing a confused or surprised face.

O RLY, interjection. (Internet slang) Expressing interest, usually with implied sarcasm or disdain.

O, noun. 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, noun. The 15th letter of the Roman alphabet.

O, noun. The blood group whose red cells carry neither the A nor B antigens; "people with type O blood are universal donors".