:being a single unit or thing
:being one in particular
- The Grand Canyon is one place I'd like to visit.
:being preeminently what is indicated
- She is one tough teacher.
:being the same in kind or quality
- "Puma" and "cougar" are different names for one animal.
:constituting a unified entity of two or more components
- The combined elements form one substance.
:being in agreement or union
- will see you again one day
:being a certain individual specified by name
- one John Doe made a speech
- the one person she wanted to marry