o

1 of 11

noun (1)

plural o's or os ˈōz How to pronounce o (audio)
often capitalized, often attributive
1
a
: 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

o

2 of 11

abbreviation (1)

1
ocean
2
ohm
3
old
4
order
5
over

O

3 of 11

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.

O

4 of 11

noun (2)

: 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

O

5 of 11

abbreviation (2)

1
offense
2
Ohio
3
[New Latin octarius] pint

O

6 of 11

symbol

oxygen

o-

7 of 11

combining form

variants or oo-
: egg
oology
specifically : ovum
oogonium

o-

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

Dictionary Entries Near o

Cite this Entry

“O.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/o. Accessed 26 Nov. 2022.

Kids Definition

o 1 of 2

noun

ˈō
often capitalized
1
: the 15th letter of the English alphabet
2

O

2 of 2

variant of oh entry 1

Medical Definition

o- 1 of 4

abbreviation

orth-; ortho-

O

2 of 4

noun

: 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

O

3 of 4

abbreviation

1
opening
2
[Latin octarius] pint
used in writing prescriptions

O

4 of 4

symbol

oxygen

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