1. In ancient and medieval philosophy, a pure, invisible substance believed to fill the upper regions of space beyond the atmosphere.
Usage: archaic; philosophical
2. In 19th-century physics, a hypothetical medium thought to fill all space and transmit light and electromagnetic waves.
Usage: historical; physics
3. The sky or upper air; the heavens.
Usage: poetic; archaic

Examples

• Ancient Greeks believed aether was the divine substance of the cosmos.
• Scientists once thought light traveled through an invisible aether that permeated space.
• The poet gazed upward into the aether, lost in contemplation.
• Einstein's theory of relativity made the concept of aether unnecessary.
• Medieval scholars debated whether aether was truly the fifth element.