(noun, adjective)


1. liable to sudden unpredictable change

- mercurial twists of temperament

Similar word(s): changeable, changeful, erratic, fickle, quicksilver

2. relating to or under the (astrological) influence of the planet Mercury

- the Mercurial canals

3. relating to or having characteristics (eloquence, shrewdness, swiftness, thievishness) attributed to the god Mercury

- more than Mercurial thievishness

4. relating to or containing or caused by mercury

- mercurial preparations

- mercurial sore mouth


1. (obsolete) Any of the plants known as mercury. [13th-17th c.]

2. (astrology) Someone born under the influence of Mercury. [from 16th c.]

3. (now historical) A preparation of mercury, especially as a treatment for syphilis. [from 17th c.]