Mer‐cu″ri‐al (?), a. [L. mercurialis, fr. Mercurius Mercury: cf. F. mercuriel.] 1. Having the qualities fabled to belong to the god Mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament.
A mercurial man
Who fluttered over all things like a fan. Byron.
2. Having the form or image of Mercury; — applied to ancient guideposts. Chillingworth.
3. Of or pertaining to Mercury as the god of trade; hence, money-making; crafty.
The mercurial wand of commerce. J. Q. Adams.
4. Of or pertaining to, or containing, mercury; as, mercurial preparations, barometer. See Mercury, 2.
5. (Med.) Caused by the use of mercury; as, mercurial sore mouth.