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the·o·ry

(thēə-rē, thîrē)

n. pl. the·o·ries

1. A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

2. The branch of a science or art consisting of its explanatory statements, accepted principles, and methods of analysis, as opposed to practice: a fine musician who had never studied theory.

3. A set of theorems that constitute a systematic view of a branch of mathematics.

4. Abstract reasoning; speculation: a decision based on experience rather than theory.

5. A belief or principle that guides action or assists comprehension or judgment: staked out the house on the theory that criminals usually return to the scene of the crime.

6. An assumption based on limited information or knowledge; a conjecture.

[Late Latin theōria, from Greek theōriā, from theōros, spectator : probably theā, a viewing + -oros, seeing (from horān, to see).]

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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