(wun) adjective
1. Being a single individual or object; being a unit.
2. Being an individual or thing thought of as indefinite.
3. Designating a person, thing, or group as contrasted with another; this; that.
4. Single in kind; the same; closely united or alike.
5. Unitary.
—noun
1. A single unit; the cardinal number preceding two; also, a symbol (1, i, I) representing this number.
2. A single thing or person.
—pron.
1. Someone or something; anyone or anything.
2. One of certain persons or things already mentioned.
—all one Of the same or of no consequence.
—at one In harmony; the same.
—one another Each other: said of an action or relation involving two or more persons or things reciprocally: They love one another.
—one by one Singly and in succession.
—one day Some indefinite day or period in the past or future. [OE ān]

Chem.
Denoting an organic compound of the ketone group: acetone. [<Gk. -ōnē, fem. patronymic]