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mer·​cu·​ri·​al (ˌ)mər-ˈkyu̇r-ē-əl How to pronounce mercurial (audio)
: of, relating to, or born under the planet Mercury
: having qualities of eloquence, ingenuity, or thievishness attributed to the god Mercury or to the influence of the planet Mercury
: characterized by rapid and unpredictable changeableness of mood
a mercurial temper
: of, relating to, containing, or caused by mercury
mercurially adverb
mercurialness noun


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: 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). He was noted for his eloquence, swiftness, and cunning, and the Romans named what appeared to them to be the fastest-moving planet in his honor. Mercurial comes from the Latin adjective mercurialis, meaning "of or relating to Mercury."

Choose the Right Synonym for mercurial

inconstant, fickle, capricious, mercurial, unstable mean lacking firmness or steadiness (as in purpose or devotion).

inconstant implies an incapacity for steadiness and an inherent tendency to change.

an inconstant friend

fickle suggests unreliability because of perverse changeability and incapacity for steadfastness.

performers discover how fickle fans can be

capricious suggests motivation by sudden whim or fancy and stresses unpredictability.

an utterly capricious critic

mercurial implies a rapid changeability in mood.

made anxious by her boss's mercurial temperament

unstable implies an incapacity for remaining in a fixed position or steady course and applies especially to a lack of emotional balance.

too unstable to hold a job

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
Recent Examples on the Web
So while the stereotype of a mercurial, borderline antisocial founder in the mold of Steve Jobs or Elon Musk might exist (and perhaps be slightly true) the study points to the fact that companies tend to penalize entrepreneurs unfairly. Paolo Confino, Fortune, 12 May 2024 But her attempts to gain a bigger role in her father’s life or at Viacom were repeatedly rebuffed by the mercurial mogul, his live-in girlfriends and even Viacom’s top brass. Meg James, Los Angeles Times, 11 May 2024 See all Example Sentences for mercurial 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'mercurial.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History



see mercury


see mercury

First Known Use


14th century, in the meaning defined at sense 1


1676, in the meaning defined above

Time Traveler
The first known use of mercurial was in the 14th century


Dictionary Entries Near mercurial

Cite this Entry

“Mercurial.” Dictionary, Merriam-Webster, Accessed 19 May. 2024.

Kids Definition


: characterized by rapid and unpredictable change of mood

Medical Definition


1 of 2 adjective
mer·​cu·​ri·​al (ˌ)mər-ˈkyu̇r-ē-əl How to pronounce mercurial (audio)
: of, relating to, containing, or caused by mercury
mercurial salves


2 of 2 noun
: a pharmaceutical or chemical containing mercury
the diuretic action of mercurials

More from Merriam-Webster on mercurial

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