mercurial

adjective

1. relating to or under the (astrological) influence of the planet Mercury"the Mercurial canals"
2. relating to or containing or caused by mercury"mercurial preparations"
3. relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury"more than Mercurial thievishness"
4. liable to sudden unpredictable change"erratic behavior"