Definition of "number one" in English

Adjective

1. First; foremost; best, often used after its headword.

   • Commuting to work is the number one reason to own a car.
   • He is my enemy number one.

2. Black, African-American.

Noun

1. The most important person, the one who is in charge.

2. Someone who is top of a ranking, who is ranked first.

3. Oneself, being considered foremost, as by an egoist.

4. Urine; urination.

5. The single that has sold the most in a given period.

6. The main goalkeeper of a team, so-called because they wear the number 1 on the back of their kit.

7. The batsman who opens the batting.

8. A first lieutenant.

9. A large town where theatrical performances may expect to achieve success.

10. Used other than figuratively or idiomatically: see number,‎ one.