Definition of mercurial

The word "mercurial" originates from the Latin word "Mercurius," the name of the Roman god of commerce, eloquence, and thievery, who was also identified with the Greek god Hermes. Mercury, the planet, was also named after this god, as it was associated with his swiftness. In the 15th century, the term "mercurial" referred to the planet Mercury or anything related to it. Over time, the term took on a more figurative meaning, describing something or someone that is changeable, unpredictable, and prone to rapid mood swings, much like the planet's quick movements across the sky. This connotation was likely influenced by the ancient myth that Mercury was a messenger of the gods, known for his quick wit and mischievous nature. Today, the word "mercurial" is often used to describe someone with a volatile personality or someone who is difficult to pin down due to their inconsistent behavior.