Meaning of THEORY in English

THEORY

/ ˈθɪəri; NAmE ˈθɪri; ˈθiːəri/ noun ( pl. -ies )

1.

[ C , U ] a formal set of ideas that is intended to explain why sth happens or exists :

According to the theory of relativity, nothing can travel faster than light.

2.

[ U ] the principles on which a particular subject is based :

the theory and practice of language teaching

3.

[ C ] theory (that) an opinion or idea that sb believes is true but that is not proved :

I have this theory that most people prefer being at work to being at home.

IDIOMS

- in theory

••

WORD ORIGIN

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

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.