| Noun | 1. | atomic number 80 - a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperaturesmetal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. cinnabar - a heavy reddish mineral consisting of mercuric sulfide; the chief source of mercury calomel, mercurous chloride - a tasteless colorless powder used medicinally as a cathartic |