Chemistry. a heavy, silver-white, highly toxic metallic element, the only one that is liquid at room temperature; quicksilver: used in barometers, thermometers, pesticides, pharmaceutical preparations, reflecting surfaces of mirrors, and dental fillings, in certain switches, lamps, and other electric apparatus, and as a laboratory catalyst. Symbol: Hg; atomic weight: 200.59; atomic number: 80; specific gravity: 13.546 at 20°C; freezing point: −38.9°C; boiling point: 357°C.
Pharmacology. this metal as used in medicine, in the form of various organic and inorganic compounds, usually for skin infections.
(initial capital letter) the ancient Roman god who served as messenger of the gods and was also the god of commerce, thievery, eloquence, and science, identified with the Greek god Hermes.
(initial capital letter) Astronomy. the planet nearest the sun, having a diameter of 3031 miles (4878 km), a mean distance from the sun of 36 million miles (57.9 million km), and a period of revolution of 87.96 days, and having no satellites: the smallest planet in the solar system.