a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves | a colorless volatile highly flammable liquid formerly used as an inhalation anesthetic |
| a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves |
| any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom |
| the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies |