1 one /ˈwʌn/ noun
plural ones
1 one
plural ones
Learner's definition of ONE
[count] US : a one-dollar bill
[count] : the first in a set or series

as one

: at the same time : all together
: in agreement with each other

at one with

: in a peaceful state as a part of something else
formal : in a state of agreement with another person

for one

: as an example

in one

: combined in a single thing

the odd one out

see odd
2 one /ˈwʌn/ pronoun
2 one
Learner's definition of ONE
: that person or thing
◊ This sense of one can be used in the plural form ones.
: someone or something that is a part of a particular group + of
somewhat formal : people in general : any person
British, old-fashioned : I or we

one after another

see 2another

one and all


one by one

: separately in a series

one in a million

see million

there's one born every minute

see born
see also no one
3 one /ˈwʌn/ adjective
3 one
Learner's definition of ONE
always used before a noun : having the value of 1
always used before a noun used to refer to a single person or thing
used before a noun to indicate that someone or something is part of a group of similar people or things
chiefly US, informal used to emphasize a description
always used before a noun : not known exactly : some
used to indicate that two or more people or things are actually the same person or are the same kind of thing
formal used before a name to indicate that you do not know the person specified
not used before a noun : in agreement with each other

the one and only

used before the name of a famous person to say that there is no one else like that person