mercurial
Say it: mur-KYOOR-ee-ul /məːˈkjʊərɪəl/ · adjective
What “mercurial” means
Having moods that change suddenly and unpredictably.
More precisely: Subject to sudden, unpredictable changes of mood.
When to use it
When someone's mood shifts sharply and unpredictably. A fairly formal description, often warning that they can be hard to deal with.
Similar words
volatile, unpredictable, temperamental
Where it comes from
From Latin mercurialis, 'of Mercury'; astrology linked the planet to a lively, changeable temperament.
Quick check
Without any clear reason, your cheerful host suddenly becomes furious, then starts laughing again minutes later. They're…
mercurial or irascible?
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mercurial
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