1. Symbol HgA silvery-white poisonous metallic element, liquid at room temperature and used in thermometers, barometers, vapor lamps, and batteries and in the preparation of chemical pesticides. Atomic number 80; atomic weight 200.59; melting point -38.83°C; boiling point 356.62°C; specific gravity 13.546 (at 20°C); valence 1, 2.Also called quicksilver. See Periodic Table.

2. Temperature:The mercury had fallen rapidly by morning.

3. Any of several weedy plants of the genera Mercurialis and Acalypha.