Did you know?

Click any word in a definition or example to find the entry for that word

theory

 - definition
 
 
 
Close

What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.

Close

Thesaurus

The thesaurus of synonyms and related words is fully integrated into the dictionary entries. Click on the T button in an entry to review the synonyms and related words for that meaning.

more
noun theory pronunciation in American English /ˈθiəri/ 
Word Forms
Close
singulartheory
pluraltheories
  1. 1
    [countable] one or more ideas that explain how or why something happens

    The theory predicts low speeds and therefore safety.

    theory that:

    He had a theory that the germs caused disease.

  2. 2
    [uncountable] the set of general principles that a particular subject is based on

    the theory and practice of education

    psychoanalytic/Marxist/literary theory

  3. 3
    [countable] an idea that you believe is true although you have no proof
    theory about:

    I have my own theory about why he resigned.

    theory that:

    There is a theory that her death was an accident.

Open Dictionary

chicken raffle

any random process, such as a competition in which a name is drawn from a hat

add a word

Blog

A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog