o

1 of 11

noun (1)

ˈō

plural o's or os ˈōz

often capitalized, often attributive

: the 15th letter of the English alphabet

: a graphic representation of this letter

: a speech counterpart of orthographic o

: a graphic device for reproducing the letter o

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

: something shaped like the letter O

especially : zero

2 of 11

abbreviation (1)

ocean

ohm

old

order

over

3 of 11

interjection

less common spelling of oh

—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!

—used in direct address

oh, waiter! Will you come here, please?

—used to express acknowledgment or understanding of a statement

Oh, yes. It's one of my favorite cities.

—used to introduce an example or approximation

Their house is about, oh, I'd say four miles from here.

4 of 11

noun (2)

ˈō

: 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

5 of 11

abbreviation (2)

offense

Ohio

[New Latin octarius] pint

6 of 11

symbol

oxygen

7 of 11

combining form

variants or oo-

: egg

oology

specifically : ovum

oogonium

8 of 11

abbreviation (3)

orth- or ortho-

-o-

9 of 11

affix

—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

10 of 11

noun suffix

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

bucko

-o

11 of 11

interjection suffix

—in interjections formed from other parts of speech

cheeriorighto

Example Sentences

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

Word History

Etymology

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

First Known Use

Noun (1)

before the 12th century, in the meaning defined at sense 1a

Noun (2)

1929, in the meaning defined above

Time Traveler

The first known use of o was before the 12th century

See more words from the same century

Cite this Entry

Style

“O.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/o. Accessed 7 Dec. 2022.

Copy Citation

Kids Definition

1 of 2 noun

ˈō

often capitalized

: the 15th letter of the English alphabet

: zero entry 1 sense 1

2 of 2

variant of oh entry 1

Medical Definition

1 of 4 abbreviation

orth-; ortho-

2 of 4 noun

ˈō

: 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

3 of 4 abbreviation

opening