Definition of "Mercurial" :

adjective: liable to sudden unpredictable change

"Mercurial twists of temperament."

adjective: relating to or containing or caused by mercury

"Mercurial preparations."

adjective: relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury

"More than Mercurial thievishness."

adjective: relating to or under the (astrological) influence of the planet Mercury

"The Mercurial canals."