being a single unit or thing

I can only find one sock

being the first of the stated kind

on page one

being a particular object or person

Close first one eye then the other

being the only individual of an indicated or implied kind

the one person who can help us

the age of 1 year

the hour one hour after midday or midnight

the first in a set or series

something having a denomination of one

I'll take the money in ones

a single person or thing

a unified entity

They all rose as one

a particular example or instance

one of the coldest nights of the year

before a name: a specified person

a book by one George Smith

a blow or stroke

hit him one on the jaw

a drink

time for a quick one

a joke or story

Have you heard this one?

an enthusiast

is rather a one for musicals

a bold, amusing, or remarkable character

Oh, you are a one!