1. The pure, highly concentrated essence of a thing.
2. The purest or most typical instance: the quintessence of evil.
3. In ancient and medieval philosophy, the fifth and highest essence after the four elements of earth, air, fire, and water, thought to be the substance of the heavenly bodies and latent in all things.
4. A form of dark energy due to a hypothetical scalar field that permeates all space, the energy density of which varies across space and time, in contrast to the cosmological constant.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.