mer·cu·ri·al
(ˌ)mər-ˈkyu̇r-ē-əl 
1
a
: characterized by rapid and unpredictable changeableness of mood
a mercurial temperament
… he has a mercurial personality, a quality that leaves him hard to predict.—
Kim Marcus
Kim Marcus
b
: very lively and quick
… the mercurial, nimble-witted types, persons given to animated speech and repartee …—A. C. Partridge
A. C. Partridge
c
: changing often : very changeable
mercurial weather
… the mercurial nature of adolescent slang.—Harry F. Waters
Harry F. Waters2
a
: having qualities (as of eloquence, ingenuity, or thievishness) attributed to the god Mercury or in astrology to the influence of the planet Mercury
… innovative mercurial cunning that can shift genes and outwit germs …—James Hillman
James Hillman
b
: fast in development or occurrence : quick
… she's so new to golf … that her mercurial rise is surprising, even to her.—Neil H. Devlin
Neil H. Devlin3
: of, relating to, or born under the planet Mercury
The iconic Gemini embodies the wit, agility, and mischief of his mercurial sign.—Holiday Mathis
Holiday Mathis4
: of, relating to, containing, or caused by mercury
mercurial preparations
mercurialness
noun
: a pharmaceutical or chemical containing mercury
Did you know?
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
Adjective
Few moments in English history have been more hungry for the future, its mercurial possibilities and its hope of richness, than the spring of 1603.
—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
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
Recent Examples on the Web
Max Zahn, ABC News, 31 Oct. 2025
Trump is famously mercurial, while Petro could become more conciliatory.
—Ellie Cook, MSNBC Newsweek, 30 Oct. 2025
Much of the businesses’ complaints stemmed from the mercurial nature of the administration’s approach to trade.
—Kate Nishimura, Sourcing Journal, 29 Oct. 2025
Hoss, whom audiences might remember as Blanchett’s violinist partner in 2022’s Tár, is a force as the outspoken, mercurial Eileen.
—Abby Monteil, Them., 28 Oct. 2025
See All Example Sentences for mercurial
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Adjective
Some trade experts who spoke with ABC News indicated both sides had won notable concessions, though the ultimate impact may depend on whether the agreement can withstand mercurial US-China relations.
—Max Zahn, ABC News, 31 Oct. 2025
Trump is famously mercurial, while Petro could become more conciliatory.
—Ellie Cook, MSNBC Newsweek, 30 Oct. 2025
Much of the businesses’ complaints stemmed from the mercurial nature of the administration’s approach to trade.
—Kate Nishimura, Sourcing Journal, 29 Oct. 2025
Hoss, whom audiences might remember as Blanchett’s violinist partner in 2022’s Tár, is a force as the outspoken, mercurial Eileen.
—Abby Monteil, Them., 28 Oct. 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 8 Nov. 2025.
Copy CitationMedical Definition
mercurial
1 of 2 adjective
mer·cu·ri·al
(ˌ)mər-ˈkyu̇r-ē-əl
: of, relating to, containing, or caused by mercury
mercurial salves
mercurial
2 of 2 noun
: a pharmaceutical or chemical containing mercury
the diuretic action of mercurials
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