having the qualities fabled to belong to the god mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament.-having the form or image of mercury; -- applied to ancient guideposts.-of or pertaining to mercury as the god of trade; hence, money-making; crafty.-of or pertaining to, or containing, mercury; as, mercurial preparations, barometer. see mercury, 2.-caused by the use of mercury; as, mercurial sore mouth.-a person having mercurial qualities.-a preparation containing mercury.