ether

(noun) the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies. Synonyms: quintessence.

(noun) any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom.

(noun) a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves. Synonyms: aether.

(noun) a colorless volatile highly inflammable liquid formerly used as an inhalation anesthetic. Synonyms: ethoxyethane, divinyl ether, vinyl ether, diethyl ether, ethyl ether.