Mercurial (adjective, noun)
mer-cu-ri-al [mer-kyoo r-ee-uh l]

adjective
1. changeable; volatile; fickle; flighty; erratic: a mercurial nature.
2. animated; lively; sprightly; quick-witted.
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
6. Pharmacology. a preparation of mercury used as a drug.

Synonyms
1. inconstant, indecisive.
2. spirited.

Antonyms
1. constant, steady.
2. phlegmatic.

Origin: 1350-1400; Middle English < Latin mercurialis of, pertaining to the god or planet Mercury. See mercury, -al

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