o

noun (1), often capitalized, often attributive

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\ ˈō

plural o's or os\ ˈōz

Definition of o

(Entry 1 of 11)

1a : the 15th letter of the English alphabet

b : a graphic representation of this letter

c : a speech counterpart of orthographic o

2 : a graphic device for reproducing the letter o

3 : one designated o especially as the 15th in order or class

4 : something shaped like the letter O especially : zero

abbreviation (1)

Definition of o (Entry 2 of 11)

1 ocean

2 ohm

3 old

4 order

5 over

interjection

less common spelling of oh

1 —used to express an emotion (such as surprise or desire) or in response to physical stimuli Oh, no! I forgot my key.Oh, don't stop!

2 —used in direct address oh, waiter! Will you come here, please?

3 —used to express acknowledgment or understanding of a statement Oh, yes. It's one of my favorite cities.

4 —used to introduce an example or approximation Their house is about, oh, I'd say four miles from here.

noun (2)

\ ˈō

Definition of O (Entry 4 of 11)

: the one of the four ABO blood groups characterized by the absence of antigens designated by the letters A and B and by the presence of antibodies against these antigens

abbreviation (2)

Definition of O (Entry 5 of 11)

1 offense

2 Ohio

3 [New Latin octarius] pint

symbol

Definition of O (Entry 6 of 11)

oxygen

combining form

variants: or oo-

Definition of o- (Entry 7 of 11)

: egg oology specifically : ovum oogonium

abbreviation (3)

Definition of o- (Entry 8 of 11)

orth- or ortho-

-o-

affix

Definition of -o- (Entry 9 of 11)

—used as a connective vowel originally to join word elements of Greek origin and now also to join word elements of Latin or other origin speedometerelastomer

-o

noun suffix

Definition of -o (Entry 10 of 11)

: one that is, has the qualities of, or is associated with bucko

-o

interjection suffix

Definition of -o (Entry 11 of 11)

—in interjections formed from other parts of speech cheeriorighto

Synonyms Example Sentences Learn More About o

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Synonyms for o

Synonyms: Noun (1)

Examples of o in a Sentence

Noun (1) a word that starts with an o a word that starts with o

History and Etymology for o

Combining form

Greek ōi-, ōio-, from ōion — more at egg entry 1

Affix

Greek, thematic vowel of many nouns and adjectives in combination

Noun suffix

perhaps from oh entry 1

Interjection suffix

probably from oh entry 1

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Dictionary Entries Near o

nytril

-nyxis

-o-

Statistics for o

Cite this Entry

“O.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/o. Accessed 17 Jun. 2021.

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More Definitions for o

noun

English Language Learners Definition of o

: the 15th letter of the English alphabet

: the number zero

—used as a mark at the end of a letter, an e-mail, etc., to represent a hug

See the full definition for o in the English Language Learners Dictionary

noun, often capitalized

\ ˈō \

plural o's or os\ ˈōz \

Kids Definition of o

1 : the 15th letter of the English alphabet

2 : zero sense 1

Kids Definition of O

variant of oh

abbreviation

Kids Definition of O.

Ohio

abbreviation

Medical Definition of o-

(Entry 1 of 4)

orth-; ortho-

noun

\ ˈō

Medical Definition of O (Entry 2 of 4)

: the one of the four ABO blood groups characterized by the absence of antigens designated by the letters A and B and by the presence of antibodies against these antigens

abbreviation

Medical Definition of O (Entry 3 of 4)

1 opening

2 [Latin octarius] pint —used in writing prescriptions

symbol

Medical Definition of O (Entry 4 of 4)

oxygen