one · pron
one by one
B2 separately, one after the other
Dictionary examples:
They entered the room one by one. (14.5)
One by one the old buildings in the city have been demolished and replaced with modern glass towers. (43.9)
one at a time
B2 separately
Dictionary examples:
Eat them one at a time. (9.2)
one after another
B2 many, in a series, especially with very little time between them
Dictionary examples:
She read all four books one after another. (10.4)
She ate the chocolates one after the other until the box was finished. (19.4)
(all) in one
C2 combined into a single thing
Dictionary examples:
It's a vacation and art course all in one. (19.2)
one (PARTICULAR PERSON/THING)
A2 used to refer to a particular person or thing in a group that has already been talked about
Dictionary examples:
Which student? The one sleeping in class. (0.0)
Which teacher? The one with funny hair. (0.0)
Which dog? The one chasing its tail. (0.0)
Which one would you like? (9.8)
"Which cupcake would you like?" "The one in the front." (27.0)
There were lots of people standing watching, and not one of them offered to help. (29.7)
I've got a few books on Chinese cooking. You can borrow one if you like. (36.4)
Would you make a copy for everybody in the office and a few extras for the visitors? (42.7)
one (ANY PERSON)
C1 any person in general
Dictionary examples:
One ought to respect one's parents. (23.0)
one another
B1 each other
Dictionary examples:
The students kept passing notes to one another during the boring lecture. (0.0)
The siblings kept blaming one another for eating the last cookie. (0.0)
The two cats chased one another around the house, knocking over everything! (0.0)
How can they reach an agreement if they won't talk to one another? (35.8)