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The Roman god Mercury was the messenger and herald of the gods and also the god of merchants and thieves (his counterpart in Greek mythology is Hermes). His swiftness inspired the Romans to give his name to what they correctly assessed as the fastest-moving planet in the solar system. Mercury’s speed also apparently made the name apt for English speakers wishing to describe those whose moods travel quickly between extremes, a meaning mercurial has had since the mid-17th century. The adjective mercurial comes from the Latin mercurialis, meaning “of or relating to Mercury.”
Examples of mercurial in a Sentence
Adam Nicolson, God's Secretaries, 2003
Though you could see all three places in one day, each of them makes you want to stay or to keep returning to watch the effects of the changing weather and the mercurial Sicilian light.
—Francine Prose, Atlantic, December 2002
Some scientists suggest that because manic-depressive patients are ever riding the bio-chemical express between emotional extremes, their brains end up more complexly wired and remain more persistently plastic than do the brains of less mercurial sorts.
—Natalie Angier, New York Times, 12 Oct. 1993
Still grinning, still miming, he samba-ed across the floor … and started in on the dishes with a vigor that would have prostrated his mercurial cousin.
—T. Coraghessan Boyle, Harper's, October 1987
the boss's mood is so mercurial that we never know how he's going to react to anything
Patrick Sauer, Smithsonian Magazine, 27 June 2025
But on this balmy May afternoon, five weeks before a critical summit with the mercurial U.S. President Donald Trump and dozens of other leaders, the question of unity hangs over the alliance.
—Adam Rasmi, Time, 20 June 2025
Layoffs and firings have sometimes felt more mercurial than anything else.
—Patrick George, The Atlantic, 18 June 2025
After months of talking up the prospects for diplomacy with Iran (and years of bemoaning past American military failures in the Middle East), the famously mercurial Trump seemed to have embraced a more hawkish view.
—Reid Smith, Foreign Affairs, 18 June 2025
See All Example Sentences for mercurial
Cite this Entry
“Mercurial.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/mercurial. Accessed 16 Jul. 2025.
Copy CitationMedical Definition
mercurial
1 of 2 adjective
mercurial
2 of 2 noun
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