Definition

1. Noun:

   • A single person or thing: The number or figure representing the lowest cardinal number; a single unit.
   • The number one: The smallest whole number or a numeral representing it.
   • A particular but unspecified person or thing: Used to refer to a person or thing of a particular type, often for emphasis.

2. Adjective:

   • Being a single unit or entity: Used before a noun to indicate a single person or thing.
   • The same: Identical; not different.
   • United or undivided: Acting or speaking in agreement.
   • Used for emphasis: Informal intensifier meaning "remarkable" or "notable."

3. Pronoun:

   • A person of a specified type: Used to refer to the speaker or to people in general.
   • A thing previously mentioned: Used to avoid repeating a noun.

Usage Examples

• Noun:

  • He is the best one. (He is the best single person/thing.)
  • This is the one I ordered. (This is the specific item I requested.)
  • They had lunch at one. (They had lunch at 1 o'clock.)

• Adjective:

  • She's one girl in a million. (She is a single, unique girl among millions.)
  • The nation is one and undivided. (The nation is a single, united entity.)
  • That is one fine dog. (That is a remarkably fine dog.)

• Pronoun:

  • If one wants to succeed, one must work hard. (If a person wants to succeed, that person must work hard.)
  • I need a pen. Do you have one? (I need a pen. Do you have a pen?)

Advanced Usage

• "The one and only": Used for emphasis to mean unique or famous.

  • She is the one and only expert on this topic. (She is the single, unparalleled expert.)

• "At one": In agreement or harmony.

  • The committee was at one on the decision. (The committee was in complete agreement.)

• "One by one": Individually and in sequence.

  • The students entered the room one by one. (The students entered individually, in order.)

Variants and Related Words

• Oneself (pronoun): A person's own self.

  • One must learn to rely on oneself. (A person must learn to be self-reliant.)

• One-off (noun/adjective): Something that happens or is made only once.

  • The concert was a one-off event. (The concert was a single, non-repeating event.)

Synonyms

• Single: Only one in number.
• Individual: A single, separate person or thing.
• Unit: A single thing or person regarded as complete.

Related Phrases (Phrasal Verbs)

• One up (on someone): To gain an advantage over someone.

  • He always tries to one up his colleagues. (He always tries to be better than his colleagues.)

• One out: (In baseball) To retire a batter.

  • The pitcher needs to one out to end the inning. (The pitcher needs to get one more batter out.)

Related Idioms

• It's all one to me: It makes no difference to me; I don't care.

  • We can go today or tomorrow; it's all one to me. (Either option is equally acceptable to me.)

• Ten to one: Very likely; almost certain.

  • Ten to one he'll be late. (It is very probable that he will be late.)

• For one: As one example (often used to emphasize a personal opinion).

  • I, for one, disagree with the plan. (I, as one person, disagree.)

Noun

1. a single person or thing
   • he is the best one
   • this is the one I ordered
2. 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

Adjective

1. 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
2. being a single entity made by combining separate components
   • three chemicals combining into one solution
3. indefinite in time or position
   • he will come one day
   • one place or another
4. used informally as an intensifier
   • that is one fine dog
5. of the same kind or quality
   • two animals of one species
6. having the indivisible character of a unit
   • a unitary action
   • spoke with one voice
7. used of a single unit or thing; not two or more
   • `ane' is Scottish