number one

Piecewise doublet of numero uno.

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number one (not comparable)

1. (idiomatic) 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.

   • 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^[1], archived from the original on 10 July 2024:

     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.

2. (US, law enforcement, slang) Black, African-American.

number one (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.
   • 1979, Robert Hazard, “Girls Just Want to Have Fun”, in She's So Unusual‎^[2], performed by Cyndi Lauper, published 1983:

     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...

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

     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.

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

     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!

4. (childish, euphemistic) Urine; urination.
   • 1953, Samuel Beckett, Watt, [Paris]: Olympia Press, →OCLC:

     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.

5. (music) The single that has sold the most in a given period.
6. (soccer) The main goalkeeper of a team, so-called because they wear the number 1 on the back of their kit.
   • 2011 January 5, Jonathan Stevenson, “Arsenal 0 - 0 Man City”, in BBC‎^[4]:

     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.

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

• number two (especially regarding the urination sense), number three, and so on

• do number one, go number one
• look out for number one
• number one with a bullet
• Christmas number one