The Collaborative International Dictionary of English v.0.48:
Theory \The"o*ry\, n.; pl. Theories. [F. th['e]orie, L.
theoria, Gr. ? a beholding, spectacle, contemplation,
speculation, fr. ? a spectator, ? to see, view. See
1. A doctrine, or scheme of things, which terminates in
speculation or contemplation, without a view to practice;
Note: "This word is employed by English writers in a very
loose and improper sense. It is with them usually
convertible into hypothesis, and hypothesis is commonly
used as another term for conjecture. The terms theory
and theoretical are properly used in opposition to the
terms practice and practical. In this sense, they were
exclusively employed by the ancients; and in this
sense, they are almost exclusively employed by the
Continental philosophers." --Sir W. Hamilton.
2. An exposition of the general or abstract principles of any
science; as, the theory of music.
3. The science, as distinguished from the art; as, the theory
and practice of medicine.
4. The philosophical explanation of phenomena, either
physical or moral; as, Lavoisier's theory of combustion;
Adam Smith's theory of moral sentiments.
Atomic theory, Binary theory, etc. See under Atomic,
Syn: Hypothesis, speculation.
Usage: Theory, Hypothesis. A theory is a scheme of the
relations subsisting between the parts of a systematic
whole; an hypothesis is a tentative conjecture
respecting a cause of phenomena.
[1913 Webster] Theosoph