Mercurial

1. Caused by the use of mercury; as, mercurial sore mouth.
2. Having the qualities fabled to belong to the god Mercury; swift; active; sprightly; fickle; volatile; changeable; as, a mercurial youth; a mercurial temperament.
3. A preparation containing mercury.
4. A person having mercurial qualities.
5. Having the form or image of Mercury; -- applied to ancient guideposts.