1
: being a single unit or thing
one day at a time
She is one year old.
2
a
: being one in particular
early one morning
The Grand Canyon is one place I'd like to visit.
b
: being preeminently what is indicated
one fine person
She is one tough teacher.
3
a
: being the same in kind or quality
both of one species
"Puma" and "cougar" are different names for one animal.
b(1)
: constituting a unified entity of two or more components
The combined elements form one substance.
(2)
: being in agreement or union
am one with you on this
4
a
: some sense 1
will see you again one day
b
: being a certain individual specified by name
one John Doe made a speech
5
: only sense 2a
the one person she wanted to marry
1
: the first whole number above zero see Table of Numbers
2
: the number denoting unity
3
a
: the first in a set or series
—often used with an attributive noun
day one
b
: an article of clothing of a size designated one
wears a one
4
: a single person or thing
has the one but needs the other
5
: a one-dollar bill
1
: a certain indefinitely indicated person or thing
saw one of his friends
2
a
: an individual of a vaguely indicated group : anyone at all
one never knows
b
—used as a third person substitute for a first person pronoun
I'd like to read more but one doesn't have the time.
3
: a single instance of a specified action
felt like belting him one—
John Casey
John Casey
Using One as a Pronoun: Usage Guide
Sense 2a is usually a sign of a formal style. A formal style excludes the participation of the reader or hearer; thus one is used where a less formal style might address the reader directly.
for the consequences of such choices, one has only oneself to thank
—Walker Gibson
Walker Gibson
This generic one has never been common in informal use in either British or American English, and people who start sentences with one often shift to another pronoun more natural to casual discourse.
when one is learning the river, he is not allowed to do or think about anything else
—Mark Twain
Mark Twain
Use of one to replace a first-person pronoun—sense 2b—has occasionally been criticized. It is more common in British English than in American.
I'm watching this pretty carefully and I hope that the issue will come up in the Lords and one may be able to speak about it
—Donald Coggan
Donald Coggan
: ketone or related or analogous compound or class of compounds
lactone
quinone
Examples of one in a Sentence
Adjective
There is one minute left in the game.
I have a few one-dollar bills in my purse.
She is one year old.
Noun
one, two, three, four, …
I don't have any ones. Can you break a five?
I'll be there at one.
Pronoun
“I'll have an iced tea, please.” “I'll have one, too.”
Their dog died, but they plan to get another one.
“You should wear the blue one.” “The one with the stripes?” “No, the other one.”
I'd like to see the ring next to that one.
Which one did you like better?
He is the one who called the police.
That's one possible answer—but not the only one.
I would like to read more, but one doesn't have the time.
Recent Examples on the Web
SI.com, 3 Aug. 2019
Decisions made by engineers today, in other words, will determine not how one car drives but how all cars drive.
—Johannes Himmelreich, BostonGlobe.com, 30 Mar. 2018
Stephanie Gravalese, Forbes.com, 15 July 2025
The Outstanding Limited or Anthology Series category is a tough one.
—EW.com, 15 July 2025
See All Example Sentences for one
Examples are automatically compiled from online sources to
show current usage.
Read More
Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Adjective
Drinkwater didn't make one appearance in a Chelsea shirt last season, whilst Bakayoko spent the season in Italy on loan at AC Milan.
—SI.com, 3 Aug. 2019
Decisions made by engineers today, in other words, will determine not how one car drives but how all cars drive.
—Johannes Himmelreich, BostonGlobe.com, 30 Mar. 2018
Noun
But food inflation is also a feeling—one that lingers longer than a 0.3% increase.
—Stephanie Gravalese, Forbes.com, 15 July 2025
The Outstanding Limited or Anthology Series category is a tough one.
—EW.com, 15 July 2025
See All Example Sentences for one
Video
Some Odd Words with ISMO: "The One-derful Won"
Comedian ISMO tries to figure out 'one' and 'two'
Cite this Entry
“One.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/one. Accessed 23 Jul. 2025.
Copy CitationKids Definition
one
1 of 3 adjective
ˈwən 
ˌwən
1
: being a single unit or thing see number
2
: being a certain unit or thing
early one morning
3
a
: being the same in kind or quality
members of one class
b
: not divided
4
: not definitely fixed or placed
will see you again one day
5
: only entry 1 sense 2a
the one person they wanted to see
one
2 of 3 noun1
: the number indicating a single unit
2
: the first in a set or series
3
: a single person or thing
has the one, but needs the other
4
: a one-dollar bill
one
3 of 3 pronoun1
: a single member or individual
saw one of your friends
2
: any person
one never knows
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