• (RP) IPA: /məːˈkjʊə.ɹɪ.əl/
• (GA) IPA: /mɝˈkjʊ.ɹi.əl/, /-ˈkjɔ-/

mercurial (plural mercurials)

1. (obsolete) Any of the plant#Noun|plants known as mercury, especially the annual mercury or French mercury (Mercurialis annua). [13th–17th c.]
2. (astrology) A person born under the influence#Noun|influence of the planet Mercury; hence, a person having an animated#Adjective|animated, lively, quick-witted or volatile character. [from 16th c.]
   • 1622, Francis, Lord Verulam, Viscount St. Alban [i.e. Francis Bacon], The Historie of the Raigne of King Henry the Seventh, […], London: Printed by W[illiam] Stansby for Matthew Lownes, and William Barret, OCLC 1086746628 ↗, pages 112–113 ↗:

     As for {smallcaps|[Lambert] Simnell}, there was not much in him, more then that hee was a handſome Boy, and did not ſhame his Robes. But this Youth (of whom wee are now to ſpeake) was ſuch a Mercuriall, as the like hath ſeldome beene knowne; and could make his owne part, if at any time hee chanced to bee out.

3. (chemistry) A chemical compound containing mercury.
4. (pharmacology, historical) A preparation of mercury, especially as a treatment for syphilis. [from 17th c.]

mercurial

1. (comparable) Having a lively or volatile character; animated#Adjective|animated, changeable, quick-witted. [from 17th c.]

   Synonyms: fickle, unpredictable

   his mercurial temperament

2. (not comparable, astrology) Pertaining to the astrological influence#Noun|influence of the planet Mercury; having the characteristic#Noun|characteristics of a person under such influence (see adjective sense 1). [from 16th c.]
3. (not comparable, astronomy) Pertaining to the planet Mercury. [from 14th c.]
   • [c. 1386–1390, John Gower, “Book VII”, in Reinhold Pauli, editor, Confessio Amantis of John Gower: Edited and Collated with the Best Manuscripts, volume III (in Middle English), London: Bell and Daldy […], published 1857, OCLC 827099568 ↗, page 130 ↗:

     The ſixte ſuende after this / By name Canis minor is. / The which ſterre is Mercuriall / By wey of kinde, and forth withall / As it is writen in the carte / Complexion he taketh of Marte.

     (please add an English translation of this quote)]

4. (not comparable, chemistry) Of or pertaining to the element mercury or quicksilver; containing mercury. [from 16th c.]
5. (not comparable, medicine) cause#Verb|Caused by the action of mercury or a mercury compound#Noun|compound.
6. (not comparable, Roman mythology) Pertaining to Mercury, the Roman#Adjective|Roman god of, among other things, commerce, financial#Adjective|financial gain#Noun|gain, communication, and thieves and trickery; hence (comparable), money-making#Adjective|money-making; crafty. [from 15th c.]
   • 1611 April (first recorded performance)​, William Shakespeare, “The Tragedie of Cymbeline”, in Mr. William Shakespeares Comedies, Histories, & Tragedies: Published According to the True Originall Copies (First Folio), London: Printed by Isaac Iaggard, and Ed[ward] Blount, published 1623, OCLC 606515358 ↗, [Act IV, scene ii], page 390 ↗, column 1:

     I know the ſhape of's Legge: this is his Hand: / His Foote Mercuriall: his martiall Thigh / The brawnes of Hercules: but his Iouiall face— / Murther in heaven?

• mercuric
• mercury
• Mercury

• French: lunatique
• German: sprunghaft
• Italian: incostante, lunatico, lunatica, mutevole, volubile
• Russian: сообрази́тельный

• Spanish: mercurial

• Spanish: mercurial

• Spanish: mercurial

• French: mercuriel, mercurielle
• German: quecksilberhaltig
• Russian: рту́тный