A rare metallic element of the aluminium group found in some minerals, as certain pyrites, and also in the lead-chamber deposit in the manufacture of sulphuric acid
a soft blue-white metal that is poisonous, used in photoelectric cells and to kill rats, mice, and insects. It is a chemical element : symbol Tl (thallos ; because it has a bright green line in its spectrum)
a soft gray 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