theory

 
Pronunciation: /ˈθɪəri/

noun (plural theories)

  • a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained: Darwin’s theory of evolution
  • a set of principles on which the practice of an activity is based: a theory of education [mass noun]: music theory
  • an idea used to account for a situation or justify a course of action: my theory would be that the place has been seriously mismanaged
  • Mathematics a collection of propositions to illustrate the principles of a subject.

Phrases

in theory

used in describing what is supposed to happen or be possible, usually with the implication that it does not in fact happen: in theory, things can only get better; in practice, they may well become a lot worse

Origin:

late 16th century (denoting a mental scheme of something to be done): via late Latin from Greek theōria 'contemplation, speculation', from theōros 'spectator'