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noun British English pronunciation: theory /ˈθɪəri/ 
Word Forms
  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.

dark pool

a method of financial trading in which share prices are hidden and not openly available to the public

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