O - definition in the American English Dictionary - Cambridge Dictionaries Online (US)

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English definition of “O”

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O

noun  us   //

O noun (LETTER)

[C] (plural O’s, Os, o’s or os) (also o) the 15th letter of the English alphabet

O noun (ZERO)

[U] (spelled the way it is often spoken) zero

O

exclamation  us   // old use

O exclamation (EMOTION)

used when addressing someone or something, or when expressing strong emotion: "O! Canada" is the Canadian national anthem.
(Definition of O from the Cambridge Academic Content Dictionary © Cambridge University Press)
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