Definition of "Mercurial" :
adjective: liable to sudden unpredictable change
"Mercurial twists of temperament."
adjective: relating to or containing or caused by mercury
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."