oh

noun

An utterance of oh; a spoken expression of surprise, acknowledgement, etc.

verb

To utter the interjection oh; to express surprise, etc.

1. Expression of surprise.

   Oh! I didn't see you there.

2. Expression of wonder, amazement, or awe.

   Oh, wow! That's amazing.

3. Expression of understanding, affirmation, recognition, or realization.

   Oh, so that's how it works.

4. A word to precede an offhand or annoyed remark.

   Oh, leave me alone.

5. A word to precede an added comment or afterthought.

   Oh, and don't forget your coat.

6. An invocation or address (similar to the vocative in languages with noun declension), often with a term of endearment.
7. Exclamation for drama or emphasis (often poetic).

   Oh, when will it end?

8. Expression of pain. See ouch.

   Oh! That hurt.

9. Space filler or extra syllable, especially in (popular) music.
10. (interrogative) Expression of mild scepticism.

    "You should watch where you're going!" "Oh?"

11. A word to mark a spoken phrase as imaginary.

    What if he says "Oh, I need to see your ID"?

noun

The letter O, o (more commonly spelled o)

1. The digit 0 (especially in representations of speech)

   My telephone number is four-double-three-two-oh-nine.