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).
[ LL theoria f. Gk theoria f. theoros spectator f. theoreo look at ]