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- The pure, highly concentrated essence of a thing.
- The purest or most typical instance: the quintessence of evil.
- 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.
- 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.