Definitions
1.AdjectiveFirst; 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."
2.AdjectiveBlack, African-American.
3.NounThe most important person, the one who is in charge.
4.NounSomeone who is top of a ranking, who is ranked first.
5.NounOneself, being considered foremost, as by an egoist.
6.NounUrine; urination.
7.NounThe single that has sold the most in a given period.
8.NounThe main goalkeeper of a team, so-called because they wear the number 1 on the back of their kit.
9.NounThe batsman who opens the batting.
10.NounA first lieutenant.
11.NounA large town where theatrical performances may expect to achieve success.
12.NounUsed other than figuratively or idiomatically: see number, one.