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

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