Mercury in Roman mythology, the Roman god of eloquence, skill, trading, and thieving, herald and messenger of the gods, presider over roads, and conductor of departed souls to Hades, who was identified with
Hermes. He is usually represented in art as a young man with winged sandals and a winged hat, and bearing the caduceus.
His function as a messenger gave rise to the use of his name in the titles of newspapers and journals, as
The Scotch Mercury of 1643. (The ‘
English Mercury (1588)’, sometimes cited as the earliest English newspaper, was in fact an 18th-century forgery.)
From late Middle English, mercury was used to denote the chemical element of atomic number 80, a heavy silvery-white metal (also called
quicksilver) which is liquid at ordinary temperatures. This application probably arose from an analogy between the fluidity of the metal at room temperature and the rapid motion held to be characteristic of the classical deity.
Mercurial was formerly used to designate those born under the planet Mercury; having the qualities (identical with those assigned to or supposed to be inspired by the god Mercury) considered to be a consequence of this, as eloquence, ingenuity, aptitude for commerce. In current usage, it means subject to sudden or unpredictable changes of mood or mind; although these qualities were originally associated with the god, the allusion is now generally understood as referring to the properties of mercury as a metal.
