Belonging to one.

Contraction of one is.

Not any person or thing whatsoever.

(colloquial) A particularly special or compatible person or thing. / (colloquial) A particular person destined to save the universe or world; the chosen one.

The person or thing.

(chiefly Britain, Commonwealth of Nations except Canada, Ireland) Alternative form of no one

A specified object, thing or person (especially one nearby or known).

A specified object, thing or person (especially one further away/over there or known or mentioned later).

As the first in a number of examples or reasons. / As a single given example, often the most obvious or important one and almost certainly enough to sway the argument, of several reasons for something.

(collectible card games) A card included in a deck only once.