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English definition of “number one”

number one

noun [U] (THE BEST)   
the most important, best, most noticeable, or most famous person or organization in a particular area of activity: She's still the world number one in tennis. I'm your number one fan.Winners and losersImportant people and describing important peopleFamous peopleWealthy people
(Definition of number one noun (THE BEST) from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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