mercurial

Definition

Subject to sudden or unpredictable changes of mood or mind; volatile and changeable. It describes someone whose temperament shifts rapidly and unpredictably.

Etymology

From Mercury, the Roman messenger god known for his quick, unpredictable movements and also the name for the liquid metal quicksilver. The planet Mercury was also named for this god due to its rapid orbit. The adjective captures the quick-changing nature associated with the god and the metal.

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