'number one' definitions:

Definition of 'number one'

From: WordNet
noun
A reference to yourself or myself etc.; `take care of number one' means to put your own interests first
noun
The first or highest in an ordering or series; "He wanted to be the first" [syn: first, number one]
noun
The first element in a countable series; "the first of the month" [syn: first, number one, number 1]

Synonyms of 'number one'

From: Moby Thesaurus