• mercurial •
Pronunciation: mêr-kyUr-ee-êl • Hear it!
Part of Speech: Adjective
Meaning: 1. Having the characteristics of the element mercury; swift, changeable, temperamental. 2. Related to the Roman god Mercury or having the characteristics imputed to him: eloquence, shrewdness, swiftness, fickleness—or a relation to commerce.
Notes: The adverb is mercurially, the noun mercuriality, and the verb is mercurialize "treat with mercury, cause to be mercurial". Other forms have been used, but have not widely survived, e.g. the adjective mercurious, and the verb mercuriate.
In Play: Today's word offers a wide array of interpretations, so be careful to use it in a clarifying context, "His lack of commercial acumen caused his mercurial slide into bankruptcy." The swiftness of the winged feet of Mercury is most often associated with this word, however: "His marriage to the CEO's daughter sent his career into a mercurial ascent." It can also mean unpredictably changeable in direction as happens to uncontained mercury: "His temperament is a bit too mercurial for a school superintendent."
Word History: While the Roman god Mercury (Mercurius) was originally associated with trade, he eventually became equated with the Greek god Hermes, he of the winged feet. The speed imputed by winged feet recommended his name to the liquid metallic element used in thermometers and batteries, otherwise known as "quicksilver". However, we still find the root of Mercury's name in commerce, merchant, and market—all from Latin mercari "to trade", a verb from the noun merx, merc- "merchandise". (We hope this less than mercurial acknowledgement of Barbara Kelly for suggesting today's word is a fair enough for her service.)