Noun:
1: ace, unity, i, 1, single, one 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"
2: one a single person or thing; "he is the best one"; "this is the one I ordered"
Adjective:
1: i, 1, ane, cardinal, one used of a single unit or thing; not two or more; "`ane' is Scottish"
2: unitary, one, united having the indivisible character of a unit; "a unitary action"; "spoke with one voice"
3: one, same of the same kind or quality; "two animals of one species"
4: extraordinary, one used informally as an intensifier; "that is one fine dog"
5: indefinite, one indefinite in time or position; "he will come one day"; "one place or another"
6: one, combined being a single entity made by combining separate components; "three chemicals combining into one solution"
7: nonpareil, unmatched, incomparable, unrivalled, one and only, one, peerless, unrivaled, matchless, uncomparable, unmatchable eminent beyond or above comparison; "matchless beauty"; "the team's nonpareil center fielder"; "she's one girl in a million"; "the one and only Muhammad Ali"; "a peerless scholar"; "infamy unmatched in the Western world"; "wrote with unmatchable clarity"; "unrivaled mastery of her art"