Meaning of THEORY in English

n. (pl. -ies)

1. a supposition or system of ideas explaining something, esp. one based on general principles independent of the particular things to be explained (opp. HYPOTHESIS) (atomic theory; theory of evolution).

2 a speculative (esp. fanciful) view (one of my pet theories).

3 the sphere of abstract knowledge or speculative thought (this is all very well in theory, but how will it work in practice?).

4 the exposition of the principles of a science etc. (the theory of music).

5 Math. a collection of propositions to illustrate the principles of a subject (probability theory; theory of equations).

Etymology: LL theoria f. Gk theoria f. theoros spectator f. theoreo look at

Oxford English vocab.      Оксфордский английский словарь.