number one

noun
1.
oneself, especially one's own well-being or interests:
to look out for number one.
2.
a person, company, etc., that is first in rank, order, or prestige:
Our team is number one.
3.
of the highest in quality, status, importance, etc.; first-rate:
a number one performance.
4.
first in rank, order, or prestige:
the number one book on the bestseller list.
5.
urination: used especially by or with reference to children.
Idioms
6.
make / do / go number one, Informal. to urinate: used especially by or with reference to children.
Origin
1830-40
Examples from the web for number one
  • The only thing they know is who's number one and who's number two.
  • Concrete, the number one construction material, is a major source of climate-warming gases.
  • That's why vaccines are the foundation's number one priority.
  • At many universities, research is the number one criteria for tenure.
  • As an organizer, ensuring this is your number one priority.
  • Nothing against business, but it was the number one major at the school.
  • High blood pressure is the number one risk factor for strokes.
  • number one is there's always potential for some type of placebo effect any time you put a needle in anyway.
  • Extracting methane from sewage should be ranked as number one solution.
  • Lower cost is the number one factor responsible for its anticipated growth, but there are trade-offs as well.
British Dictionary definitions for number one

number one

noun
1.
the first in a series or sequence
2.
an informal phrase for oneself, myself to look after number one
3.
(informal) the most important person; leader, chief: he's number one in the organization
4.
(informal) the bestselling pop record in any one week
5.
(euphemistic) the act or an instance of urination
6.
a haircut in which the hair is cut very close to the head with an electric shaver
adjective
7.
first in importance, urgency, quality, etc: number one priority
8.
(informal) (of a pop record) having reached the top of the charts
Slang definitions & phrases for number one

Number One

noun phrase
  1. One's own self, esp as competitive with others; numero uno: Always look out for Number One, he says (1704+)
  2. Urination (1902+)
verb

: The little kid had to number one real bad