one

(informal) very; used informally as an intensifier.

“that is one fine dog”

Having the indivisible character of a unit.

“spoke with one voice”

Used of a single unit or thing; not two or more.

Eminent beyond or above comparison.

“she's one girl in a million”

“the one and only Muhammad Ali”

Being a single entity made by combining separate components.

“three chemicals combining into one solution”

Indefinite in time or position.

“he will come one day”

“one place or another”

Of the same kind or quality.

“two animals of one species”

The smallest whole number or a numeral representing this number.

“he has the one but will need a two and three to go with it”

“they had lunch at one”

A single person or thing.

“he is the best one”

“this is the one I ordered”