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O¹

(ō)

interj.

1. Used before the name of or a pronoun referring to a person or thing being formally addressed: "How can I put it to you, O you who prepare to travel with important matters on your mind?" (Jo Durden-Smith).

2. Used to express surprise or strong emotion: "O how I laugh when I think of my vague indefinite riches" (Henry David Thoreau).

O²

The symbol for oxygen.

O³

abbr.

1. Sports

a. offense

b. offensive

2. office telephone number

3. Baseball out

4. outside

5. outstanding

6. Sports overtime

abbr.

1. ocean

2. Ohio

abbr.

1. Latin octarius (pint)

2. also O. octavo

o or O

(ō)

n. pl. o's or O's also os or Os

1. The 15th letter of the modern English alphabet.

2. Any of the speech sounds represented by the letter o.

3. The 15th in a series.

4. Something shaped like the letter O.

5. O One of the four major blood groups in the ABO system. Individuals with this blood group have neither A nor B antigens on the surface of their red blood cells, and have both anti-A and anti-B antibodies in their blood serum.

6. A zero.

(click for a larger image)

brass marker, Bourbon Street

Named for the royal house ruling France when New Orleans was founded in 1718, Bourbon Street runs through the heart of the city's French Quarter.

(ə)

prep.
Informal

Of: lots o' luck; top o' the morning.

[Middle English o, a, shortening of of; see OF.]

-o-

Used as a connective to join word elements: acidophilic.

[Middle English, from Old French, from Latin, from Greek, thematic vowel of nouns and adjectives used in combination.]

-o

suff.

Used to form an informal, abbreviated, or slang word or variant: ammo.

[Perhaps from OH¹ and from shortenings such as HIPPO.]

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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