number one

1. idiomaticnot comparableFirst; foremost; best, often used after its headword.

   He is my enemy number one.

   2 more examples

   Commuting to work is the number one reason to own a car.

   Road safety is a daily tragedy that doesn’t seem to make the front pages even though it’s a number one killer. In some countries, it causes more deaths than small firearms, and in others, more than illnesses.

   2024 July 8, Lotte Knudsen, quotee, “Road crashes: a silent killer”, in Delegation of the European Union to the UN and other international organisations in Geneva, archived from the original on 10 Jul 2024

2. USnot comparableslanggovernmentBlack, African-American.

plural number ones

1. The most important person, the one who is in charge.
2. Someone who is top of a ranking, who is ranked first.

   Djokovic came through 6-4 6-1 1-6 6-3 to end Nadal's reign as Wimbledon champion, before overtaking the Spaniard as world number one on Monday.

   2011 July 3, Piers Newbury, “Wimbledon 2011: Novak Djokovic beats Rafael Nadal in final”, in BBC Sport

   1 more example

   The phone rings, in the middle of the night / My father yells "what you gonna do with your life" / Oh, daddy, dear, you know you're still number one / But girls, they wanna have fun / Oh, girls just wanna have...

   1979, Robert Hazard, “Girls Just Want to Have Fun”, in She's So Unusual, performed by Cyndi Lauper, published 1983

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

   No man should have more than two attachments—the first, to number one, and the second to the ladies; that's what I say—ha! ha!

   1836 March – 1837 October, Charles Dickens, “(please specify the chapter name)”, in The Posthumous Papers of the Pickwick Club, London: Chapman and Hall, […], published 1837, →OCLC

4. childisheuphemisticUrine; urination.

   He might have got up, without the bell's sounding, to do his number one, or number two, in his great big white chamber-pot.

   1953, Samuel Beckett, Watt, [Paris]: Olympia Press, →OCLC

5. entertainmentThe single that has sold the most in a given period.
6. ball gamesThe main goalkeeper of a team, so-called because they wear the number 1 on the back of their kit.

   England number one Hart produced a magnificent moment to deny Van Persie once more just after the hour mark, leaping across his goal to fingertip the Dutchman's crashing 25-yard, top corner-bound drive away.

   2011 January 5, Jonathan Stevenson, “Arsenal 0 - 0 Man City”, in BBC

7. ball gamesThe batsman who opens the batting.
8. A first lieutenant.
9. entertainmentA large town where theatrical performances may expect to achieve success.
10. Used other than figuratively or idiomatically: see number, one.

1. A locality in the MidCoast council area, eastern New South Wales, Australia.