mercurial

Meaning

Adj

1. Having a lively or volatile character; animated, changeable, quick-witted.
2. Pertaining to the astrological influence of the planet Mercury; having the characteristics of a person under such influence (see adjective sense 1).
3. Pertaining to the planet Mercury.
4. Of or pertaining to the element mercury or quicksilver; containing mercury.
5. Caused by the action of mercury or a mercury compound.
6. Pertaining to Mercury, the Roman god of, among other things, commerce, financial gain, communication, and thieves and trickery; hence (comparable), money-making; crafty.

Noun

1. (obsolete) Any of the plants known as mercury, especially the annual mercury or French mercury (Mercurialis annua).
2. A person born under the influence of the planet Mercury; hence, a person having an animated, lively, quick-witted or volatile character.
3. A chemical compound containing mercury.
4. A preparation of mercury, especially as a treatment for syphilis.

Synonyms

fickle

volatile

mercuric

quicksilver

inconstant

erratic

unstable

mercury

lively

quick

variable

crisp

dapper

dashing

flighty

floating

fluctuating

frisky

gay

grig

impetuous

insincere

jaunty

lightsome

live

lurid

mercurous

mobile

moody

mutable

peppy

perky

poignant

protean

quick-witted

racy

tergiversator

uncertain

unpredictable

unsettled

vagarious

vibrant

vivacious

vivid

voluble

whiffler

zippy

chameleonic

ready-witted

erratical

off the deep end

bobbish

volage

bouncing

breezy

brisk

buoyant

buxom

capricious

changeable

changeful

cheery

chipper

Hyphenated as

mer‧cu‧ri‧al

Pronounced as (IPA)

/məːˈkjʊə.ɹɪ.əl/

Etymology

Inherited from Middle English: mercurial

Cognate with Middle English: mercurial

In summary

Noun sense 1 (“(obsolete) plant known as mercury”) is from Middle English mercurial, from Anglo-Norman mercurial and Old French mercurial, or directly from their etymon, from Mercurius (“the Roman god Mercury”) + -ālis (suffix forming adjectives of relationship from nouns).
Later adjective and noun uses may have been directly derived from Latin mercuriālis, whence Middle English mercurial (“under the astrological influence of the planet Mercury”).