1. (

• quintessence ,
• ether ,

) the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies ;

2. (

• ether

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

3. (

• ether ,
• aether

) a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves ;

4. (

• ether ,
• ethoxyethane ,
• divinyl_ether ,
• vinyl_ether ,
• diethyl_ether ,
• ethyl_ether

) a colorless volatile highly flammable liquid formerly used as an inhalation anesthetic ;