Cambridge Dictionaries online Cambridge Dictionaries online

The most popular online dictionary and thesaurus for learners of English


English definition of “number theory”

number theory

noun [U]  /ˈnʌm·bər ˌθɪər·i/
mathematics the study of the qualities and characteristics of numbers
(Definition of number theory noun from the Cambridge Academic Content Dictionary © Cambridge University Press)

Word of the Day


a situation in which two people are friends

Word of the Day


Read our blog about how the English language behaves.

Learn More

New Words

Find words and meanings that have just started to be used in English, and let us know what you think of them.

Learn More