The medium postulated to carry electromagnetic waves, similar to the way a gas carries sound waves.

1. One of a class of organic compounds characterized by the structural feature of an oxygen linking two hydrocarbon groups (such as R-O-R).

2. (C₂H₅)₂O A colorless liquid, slightly soluble in water; used as a reagent, intermediate, anesthetic, and solvent. Also known as ethyl ether.