PARTICULAR PERSON/THING › used to refer to a particular person or thing in a group that has already been talked about: I've just made some scones, do you want one? Throw those gloves away and get some new ones. Chris is the one with glasses.
GENERAL formal › any person in general: One ought to respect one's parents.
one at a time › separately: Eat them one at a time.
one by one › separately, with one thing happening after another: One by one the old buildings have been demolished.
one another › each other: How can they reach an agreement if they won't talk to one another?
(all) in one › combined into a single thing: It's a vacation and art course all in one.