Definition of: theory

(thē′ər·ē, thir′ē) noun plural ·ries
1. A plan or scheme existing in the mind only, but based on principles verifiable by experiment or observation.
2. A body of the fundamental principles underlying a science or the application of a science: the theory of relativity.
3. Abstract knowledge of any art, as opposed to the practice of it.
4. A proposed explanation or hypothesis designed to account for any phenomenon.
5. Loosely, mere speculation or hypothesis; an individual idea or guess.
6. Math. An arrangement of results, or a body of theorems, presenting a systematic view of some subject: the theory of functions.
7. The science of musical composition, as distinguished from the art of execution. See synonyms under HYPOTHESIS, IDEA. [<F théorie <Gk. theōria view, speculation <theōreein look at]