noun (n)

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

  Synonym:
  quintessence
  

  source: wordnet30
• any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom(noun.substance)

  source: wordnet30
• a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves(noun.communication)

  Synonym:
  aether
  

  source: wordnet30
• a colorless volatile highly inflammable liquid formerly used as an inhalation anesthetic(noun.artifact)

  Synonym:
  diethyl ether, divinyl ether, ethoxyethane, ethyl ether, vinyl ether
  

  source: wordnet30
• A medium of great elasticity and extreme tenuity, supposed to pervade all space, the interior of solid bodies not excepted, and to be the medium of transmission of light and heat; hence often called luminiferous ether.(noun)

  source: webster1913