ether has 7 distinct synonyms spread across 3 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies
any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom
a colorless volatile highly flammable liquid formerly used as an inhalation anesthetic
Synonyms, antonyms and the broader and narrower relations for ether come from Princeton University’s WordNet. Full sources and licences.