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1. often Mercurial
a. Roman Mythology Of or relating to the god Mercury.
b. Astronomy Of or relating to the planet Mercury.
2. Having the characteristics of eloquence, shrewdness, swiftness, and thievishness attributed to the god Mercury.
3. Containing or caused by the action of the element mercury.
4. Quick and changeable in temperament; volatile: a mercurial nature.
A pharmacological or chemical preparation containing mercury.

[Middle English, of the planet Mercury, from Latin mercuriālis, of the god or planet Mercury, from Mercurius, Mercury.]

mer·cu′ri·al·ly adv.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in periodicals archive ?
If we accept that yoga itself is slippery and multi-faceted, yoga therapy is perhaps mercurially difficult to pin down.
After mercurially manoeuvring fans to the edge of their seats, it was no surprise that Traore received the Supporters' Player of the Year award.
Weisz, a talented performer whose face can mercurially reconfigure itself from smouldering beauty to deep sorrow, has perfect chemistry with McAdams, who plays a timid and quietly distressed teacher in a Jewish girls' school.
Among these the ones considered critical are: Gross lack of resources to deal with a daunting and mercurially dynamic situation, weak management of human and financial resources and serious trust deficit between public and police.
Here they played with the kind of reckless abandon that is worthy of a side this mercurially talented.
Verdict: Another whose playing career has regressed since leaving the so-called Galacticos, the mercurially talented 'Super Gav's' best days occurred when he was at the Ospreys.
"Our lessons mimicked the huge range of delights on Robin's wall, with discussions flitting mercurially between music, art, philosophy, history, poetry, and back to music again.