MERCURIAL
erratic, fickle, mercurial, quicksilver
(adjective) liable to sudden unpredictable change; “erratic behavior”; “fickle weather”; “mercurial twists of temperament”; “a quicksilver character, cool and willful at one moment, utterly fragile the next”
mercurial
(adjective) relating to or containing or caused by mercury; “mercurial preparations”; “mercurial sore mouth”
Mercurial
(adjective) relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury; “more than Mercurial thievishness”
Mercurial
(adjective) relating to or under the (astrological) influence of the planet Mercury; “the Mercurial canals”
Source: WordNet® 3.1
Etymology
Noun
mercurial (plural mercurials)
(obsolete) Any of the plants known as mercury, especially the annual mercury or French mercury (Mercurialis annua). [13th–17th c.]
(astrology) A person born under the influence of the planet Mercury; hence, a person having an animated, lively, quick-witted or volatile character. [from 16th c.]
(chemistry) A chemical compound containing mercury.
(pharmacology, historical) A preparation of mercury, especially as a treatment for syphilis. [from 17th c.]
Adjective
mercurial (comparative more mercurial, superlative most mercurial)
(comparable) Having a lively or volatile character; animated, changeable, quick-witted. [from 17th c.]
Synonyms: fickle, unpredictable
(not comparable, astrology) Pertaining to the astrological influence of the planet Mercury; having the characteristics of a person under such influence (see adjective sense 1). [from 16th c.]
(not comparable, astronomy) Pertaining to the planet Mercury. [from 14th c.]
(not comparable, chemistry) Of or pertaining to the element mercury or quicksilver; containing mercury. [from 16th c.]
(not comparable, medicine) Caused by the action of mercury or a mercury compound.
(not comparable, Roman mythology) Pertaining to Mercury, the Roman god of, among other things, commerce, financial gain, communication, and thieves and trickery; hence (comparable), money-making; crafty. [from 15th c.]
Notes
Source: Wiktionary
Mer*cu"ri*al, a. Etym: [L. mercurialis, fr. Mercurius Mercury: cf. F.
mercuriel.]
1. Having the qualities fabled to belong to the god Mercury; swift;
active; sprightly; fickle; volatile; changeable; as, a mercurial
youth; a mercurial temperament.
A mercurial man Who fluttered over all things like a fan. Byron.
2. Having the form or image of Mercury; -- applied to ancient
guideposts. [Obs.] Chillingworth.
3. Of or pertaining to Mercury as the god of trade; hence, money-
making; crafty.
The mercurial wand of commerce. J. Q. Adams.
4. Of or pertaining to, or containing, mercury; as, mercurial
preparations, barometer. See Mercury, 2.
5. (Med.)
Definition: Caused by the use of mercury; as, mercurial sore mouth.
Mer*cu"ri*al, n.
1. A person having mercurial qualities. Bacon.
2. (Med.)
Definition: A preparation containing mercury.
Source: Webster’s Unabridged Dictionary 1913 Edition