[mer.cu.ry] n, pl -ries [L Mercurius, Roman god and the planet] 1 a cap: a Roman god of commerce, eloquence, travel, cunning, and theft who serves as messenger to the other gods--compare hermes b often cap, archaic: a bearer of messages or news or a conductor of travelers
2. [ME mercurie, fr. ML mercurius, fr. L, the god] a: a heavy silver-white poisonous metallic element that is liquid at ordinary temperatures and is used esp. in scientific instruments--called also quicksilver b: the mercury in a thermometer or barometer 3 cap: the planet nearest the sun