Having the qualities fabled to belong to the god Mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament
relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury; "more than Mercurial thievishness"
relating to or containing or caused by mercury; "mercurial preparations"; "mercurial sore mouth" relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury; "more than Mercurial thievishness" relating to or under the (astrological) influence of the planet Mercury; "the Mercurial canals
relating to or under the (astrological) influence of the planet Mercury; "the Mercurial canals
relating to or containing or caused by mercury; "mercurial preparations"; "mercurial sore mouth"
relating to or under the (astrological) influence of the planet Mercury; "the Mercurial canals"
If you describe someone as mercurial, you mean that they frequently change their mind or mood without warning. his mercurial temperament. = volatile
liable to sudden unpredictable change; "erratic behavior"; "fickle weather"; "mercurial twists of temperament"; "a quicksilver character, cool and willful at one moment, utterly fragile the next"