Definition of mercurial :
1. A person having mercurial qualities.
2. A preparation containing mercury.
3. Caused by the use of mercury; as, mercurial sore mouth.
4. Having the form or image of Mercury; - applied to ancient guideposts.
5. Having the qualities fabled to belong to the god Mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament.
6. Of or pertaining to, or containing, mercury; as, mercurial preparations, barometer. See Mercury, 2.
changeable (part of speech: adjective)
inconstant, unsteady, flexible, alterable, restless, adaptable, irresolute, unsettled, vacillating, modifiable, transposable, varying, precarious, movable, shifting, convertible, mutable, protean, wavering, variable, adjustable, fluid, changeable, reformable, unstable, vicissitudinous, fickle, changeful, volatile, versatile, flighty, transformable, ever-changing
- And Fullaway, active and mercurial though he was, made no attempt at conversation- he sat with knitted forehead, trying to think, to account, to surmise, only conscious that he was up against a bigger mystery than life had ever shown him up to then. - "The Rayner-Slade Amalgamation", J. S. Fletcher.
- Poor Larry O'Hale could not thus calm his mercurial spirit. - "Sunk at Sea", R.M. Ballantyne.
- While he stormed on, saying things that he would willingly have taken back a minute later, every bit of its usual mercurial humor drained out of Billy's face. - "The Mystery of The Barranca", Herman Whitaker.