Aethers

Part of speech: noun

Definitions

1. A rarefied or ethereal substance believed to fill the universe beyond the terrestrial sphere
2. A historical concept referring to the upper regions of air, often associated with the heavens or celestial realms
3. In classical philosophy, an element thought to be the fifth essence that is essential to the nature of the universe and embodies purity

Etymology: "Aethers" is the plural of "aether," a noun whose history runs back to ancient Greek cosmology, where the upper air was thought to be a purer, brighter substance than the ordinary air below. The plural is less common in ordinary use than the singular, and it usually turns up when writers want to speak of several separate realms or kinds of this substance rather than one undifferentiated medium. The singular "aether" is itself the English form of the Greek "aither," which described the bright, clear upper air where the gods were imagined to dwell, distinct from the murkier "aer," the lower air people breathed. Later natural philosophers adopted the term for the invisible medium they believed filled the heavens beyond the terrestrial sphere, a substance meant to carry light and planetary motion through empty space.