Dictionary.com
Thesaurus.com
Synonyms

mercurial

American  
[mer-kyoor-ee-uhl] / mərˈkyʊər i əl /

adjective

  1. changeable; volatile; fickle; flighty; erratic.

    a mercurial nature.
    Synonyms:
    indecisive, inconstant
    Antonyms:
    steady, constant

  2. animated; lively; sprightly; quick-witted.

    Synonyms:
    spirited
    Antonyms:
    phlegmatic

  3. pertaining to, containing, or caused by the metal mercury.

  4. (initial capital letter) of or relating to the god Mercury.

  5. (initial capital letter) of or relating to the planet Mercury.

noun

  1. Pharmacology. a preparation of mercury used as a drug.

mercurial British  
/ mɜːˈkjʊərɪəl /

adjective

  1. of, like, containing, or relating to mercury

  2. volatile; lively

    a mercurial temperament

  3. (sometimes capital) of, like, or relating to the god or the planet Mercury

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

noun

  1. med any salt of mercury for use as a medicine

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Word Forms

  • mercuriality noun
  • mercurially adverb
  • mercurialness noun
  • unmercurial adjective
  • unmercurially adverb
  • unmercurialness noun

Etymology

Origin of mercurial

First recorded in 1350–1400; Middle English, from Latin mercuriālis “of or pertaining to the god or planet Mercury”; mercury, -al 1

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Master of the trivela, lover of a rabona - mercurial and erratic, but show-stoppingly skilful.

From BBC • Mar. 24, 2026

In recent years, the mercurial superstar has faced a number of public and legal dramas.

From Los Angeles Times • Mar. 11, 2026

Still, China is treading carefully because one of the biggest calculations for them is the mercurial US president, who is due to arrive for a much-awaited meeting later this month.

From BBC • Mar. 5, 2026

Capital Group ascended to the No. 1 spot by taking advantage of mercurial markets and seeing long-term bets pay off.

From Barron's • Feb. 26, 2026

A battle raged between two titans: the professor Booker T. Washington and the brilliant, mercurial, and quarrelsome W. E. B. Du Bois.

From "The Best of Enemies" by Osha Gray Davidson

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.