e·qua·tion (ĭ-kwāzhən, -shən)
1. The act or process of equating or of being equated.
2. The state of being equal.
3. Mathematics A statement asserting the equality of two expressions, usually written as a linear array of symbols that are separated into left and right sides and joined by an equal sign.
4. Chemistry A representation of a chemical reaction, usually written as a linear array in which the symbols and quantities of the reactants are separated from those of the products by an arrow or a set of opposing arrows.
5. A complex of variable elements or factors: "The world was full of equations ... there must be an answer for everything, if only you knew how to set forth the questions" (Anne Tyler).
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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:
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.