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English definition of “number one”

number one

noun [U] uk   us  

number one noun [U] (YOURSELF)

(US also numero uno) informal yourself and no one else: Frank is completely selfish - he only cares about number one. I'm going to look out for number one (= take care of myself only).

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.
(Definition of number one from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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