being or amounting to a single unit or individual or entire thing, item, or object rather than two or more; a single

one woman; one nation; one piece of cake.

being a person, thing, or individual instance or member of a number, kind, group, or category indicated

one member of the party.

existing, acting, or considered as a single unit, entity, or individual.

of the same or having a single kind, nature, or condition

We belong to one team; We are of one resolve.

noting some indefinite day or time in the future

You will see him one day.

a certain (often used in naming a person otherwise unknown or undescribed)

One John Smith was chosen.

being a particular, unique, or only individual, item, or unit

I'm looking for the one adviser I can trust.

noting some indefinite day or time in the past

We all had dinner together one evening last week.

of no consequence as to the character, outcome, etc.; the same

It's all one to me whether they go or not.

the first and lowest whole number, being a cardinal number; unity.

a symbol of this number, as 1 or I.

a single person or thing

If only problems would come one at a time!

a die face or a domino face having one pip.

a one-dollar bill

to change a five-dollar bill for five ones.

( initial capital letter ) Neoplatonism . the ultimate reality, seen as a central source of being by whose emanations all entities, spiritual and corporeal, have their existence, the corporeal ones containing the fewest of the emanations.

a person or thing of a number or kind indicated or understood

one of the Elizabethan poets.

(in certain pronominal combinations) a person unless definitely specified otherwise

every one.

(with a defining clause or other qualifying words) a person or a personified being or agency

the evil one; the one I love.

any person indefinitely; anyone

as good as one would desire.

Chiefly British . (used as a substitute for the pronoun I)

Mother had been ailing for many months, and one should have realized it.

a person of the speaker's kind; such as the speaker himself or herself

to press one's own claims.

something or someone of the kind just mentioned

The portraits are fine ones. Your teachers this semester seem to be good ones.

something available or referred to, esp. in the immediate area

Here, take onethey're delicious. The bar is open, so have one on me!

at one

in a state of agreement; of one opinion.

united in thought or feeling; attuned

He felt at one with his Creator.

one and all

everyone

They came, one and all, to welcome him home.

one by one

singly and successively

One by one the children married and moved away.

one for the road. road ( def. 9 ) .