<p><strong>Adjective</strong></p><ul><li>Changeable; volatile; fickle; flighty; erratic: a mercurial nature.</li><li>Synonyms: indecisive, inconstant.</li><li>Antonyms: steady, constant.</li><li>Animated; lively; sprightly; quick-witted.</li><li>Synonyms: spirited.</li><li>Antonyms: phlegmatic.</li><li>Pertaining to, containing, or caused by the metal mercury.</li><li>(Initial capital letter) of or relating to the god Mercury.</li><li>(Initial capital letter) of or relating to the planet Mercury.</li></ul><p><strong>Noun</strong></p><ul><li>Pharmacology: a preparation of mercury used as a drug.</li></ul>