- Volatile; erratic; unstable; flighty; fickle or changeable in temperament.
- Lively; clever; sprightly; animated; quick-witted. ‘I have a mercurial wit.’
- Having characteristics attributed to the Shakespeare character Mercutio, such as volatile, erratic, unstable, and shrewdness.
- Of, or pertaining to the element mercury; containing mercury; caused by the action of mercury or quicksilver.
- Having characteristics attributed to the Roman god Mercury, such as swiftness, eloquence, shrewdness, and thievishness.
- In Roman mythology, of or pertaining to the Roman god Mercury.
- In astronomy, of or pertaining to the planet Mercury; under the supposed astrological influence of the planet Mercury.