n.1. One that is first in rank, order, or importance.
2. Slang One's own interests; oneself: watching out for number one.
3. Informal a. The act of urinating.
b. Urine.
adj.1. First in rank, order, or importance: the number one team in the nation; our number one problem.
2. Foremost in quality; first-rate: bought some number one farmland.