An Encylopedia Britannica Company

number one

1 number one noun
or No. 1
1 number one
noun
or No. 1
Britannica Dictionary definition of NUMBER ONE
[noncount]
: a person, thing, or position that is highest in rank : the most important person or thing in a group of people or things
: the most successful person or thing in a group of people or things
: your own happiness, health, or success : yourself
informal : liquid waste from the body : urine used mainly by children or when speaking to children compare number two
2 number one adjective
or No. 1
2 number one
adjective
or No. 1
Britannica Dictionary definition of NUMBER ONE
: highest in rank or importance