• (Of a person) Subject to sudden or unpredictable changes of mood or mind.
  • Of or containing the element mercury.
  • (Mercurial) Of the planet Mercury.

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Example Sentences

“I can be quite mercurial if I haven’t had at least two cups of coffee.” 

“Mercurial thermometers for home use are being phased out by safer digital replacements.”

“Since Mercury is so close to the sun, the Mercurial year is only 88 days.”

Word Origin

Latin, mid-17th century

Why this word?

The adjective “mercurial” can apply to several senses of “mercury.” For example, it can describe a relation to the element mercury, a metal in liquid form at room temperature. That chemical was named after the planet Mercury, so when “Mercurial” is used to describe things relative to the planet, it is capitalized. But when the adjective is applied to a person, it’s befitting someone who is often quick-tempered and prone to sudden changes in mood.

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