one (Noun) — The smallest whole number or a numeral representing this number. ex. "he has the one but will need a two and three to go with it" ex. "they had lunch at one"
one (Noun) — A single person or thing. ex. "he is the best one" ex. "this is the one I ordered"
one (Adjective) — Used of a single unit or thing; not two or more.
one (Adjective) — Having the indivisible character of a unit. ex. "spoke with one voice"
one (Adjective) — Of the same kind or quality. ex. "two animals of one species"
one (Adjective) — Used informally as an intensifier. ex. "that is one fine dog"
one (Adjective) — Indefinite in time or position. ex. "he will come one day" ex. "one place or another"
one (Adjective) — Being a single entity made by combining separate components. ex. "three chemicals combining into one solution"
one (Adjective) — Eminent beyond or above comparison. ex. "she's one girl in a million" ex. "the one and only Muhammad Ali"
one (Pronoun) — A person in general. ex. "can one swim there?"
one (Pronoun) — A specified thing. ex. "the one on top"