a soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores
A metallic chemical element (symbol Tl) with atomic number 81: a gray post-transition metal that discolors when exposed to air.
The name thallium comes from the Ancient Greek word thallós, meaning "green branch," which was chosen to describe the green color of its radiation spectra. The suffix -ium was added to form the element's name.