thallium Meaning, Definition & Usage

  1. noun 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
    atomic number 81; Tl.

WordNet

Thal"li*um noun
Etymology
NL., fr. Gr. young or green shoot or branch, twig. So called from a characteristic bright green line in its spectrum.
Definitions
  1. (Chem.) 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. It is isolated as a heavy, soft, bluish white metal, easily oxidized in moist air, but preserved by keeping under water. Symbol Tl. Atomic weight 203.7.

Webster 1913