Ether might refer to:
- Ether (chemistry): A functional group in organic chemistry, often used as a part anesthetic and often very volatile and flammible.
- Luminiferous aether: Also known as the aether or ether. Originally theorised as the material that composed the universe. The existence of the luminiferous aether was disproved by the Michelson-Morley experiment in 1887.
- Ether (classical element): Originating with Aristotle, aether was "quintessence" or "essence" and was a pure, fifth heavenly element which the gods breathed.
- Aether (mythology): The personification (i.e., an "elemental god") of the upper sky, space and heaven. The aether of 19th century physics and the classical element is named after this god.
- Ethernet, a medium-access protocol sublayer named after the luminiferous aether.