o

1 of 11

noun (1)

ˈō 

plural o's or os ˈōz 

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)

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

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

speedometer

elastomer

-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

cheerio

righto

Synonyms

Noun (1)

• aught
• cipher
• goose egg
• naught
• nought
• nil
• nothing
• oh
• zero
• zilch
• zip

Examples of o in a Sentence

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

Phrases Containing o

• six-o-six

• six-o-six

Kids Definition

o

1 of 2 noun

ˈō

often capitalized

1

: the 15th letter of the English alphabet

2

: zero entry 1 sense 1

O

2 of 2

variant of oh entry 1

Medical Definition

o-

1 of 4 abbreviation

orth-; ortho-

O

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

O

3 of 4 abbreviation

1

opening

2

[Latin octarius] pint

—used in writing prescriptions

O

4 of 4 symbol

oxygen