[capitalized] Pertaining to the god Mercury; having the form or qualities attributed to Mercury. His foot Mercurial, his Martial thigh. Shak., Cymbeline, iv. 2. 310.To see thee yong, yet manage so thine armes, Have a mercuriall mince and martiall hands. Stirling, A Parænesis to Prince Henry.
Like Mercury in character; having the moral or mental qualities ascribed to the god Mercury, or supposed by astrologists to belong to those under his star, the planet Mercury; light-hearted; gay; active; sprightly; flighty; fickle; changeable; volatile. He is … of a disposition, perhaps, rather too mercurial for the chamber of a nervous invalid. Barham, Ingoldsby Legends, I. 201.Mercurial races are never sublime. De Quincey, Secret Societies, ii.
Pertaining to Mercury as god of trade; hence, pertaining to trade or money-making: as, mercurial pursuits. His [Monson's] mind being more martial than mercurial, … he applied himself to sea-service. Wood, Athenæ Oxon., I.Properties pertaining to the practice of the law, as well as to the mercurial profession. P. Whitehead, Gymnasiad, i., note.
Having the qualities fabled to belong to the god Mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament.
I found when I went to Grand Rapids that the intermittent, remittent, and pernicious fevers, which prevailed in that place and in the surrounding country, were generally treated by the resident physicians with mercurial or other cathartic remedies, followed or accompanied by Quinine and brandy or fermented drinks containing Alcohol, and opiates where they were supposed to be necessary.
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Personal Experience of a Physician
The frivolous and the mercurial were not in Calvin's make-up.
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Little Journeys to the Homes of Great Reformers
Meanwhile Carl's character was forming, and he was becoming as brilliant as the mercurial life he was leading, and at the same time as irresponsible.
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The Love Affairs of Great Musicians
The barstools on this invisible divide were always empty, a no-man's land.
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Ellery Queen Mystery Magazine
"I also counseled caution, which you unwisely ignored.
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Stormwarden
= Frenchmercuriel = SpanishPortuguesemercurial = Italianmercuriale, from LatinMercurialis, of or pertaining to the god Mercury or to the planet Mercury, from Mercurius, Mercury: see Mercury.