from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A soft, malleable, highly toxic metallic element, used in photocells, infrared detectors, low-melting glass, and formerly in rodent and ant poisons. Atomic number 81; atomic weight 204.38; melting point 303.5°C; boiling point 1,457°C; specific gravity 11.85; valence 1, 3. See Table at element.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A metallic chemical element (symbol Tl) with atomic number 81.

from the GNU version of the Collaborative International Dictionary of English

  • n. 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.

from The Century Dictionary and Cyclopedia

  • n. Chemical symbol, Tl; atomic weight, 204.2. A rare metal which was discovered in the residuum left from the distillation of selenium by Crookes, in 1861, and was first supposed to contain tellurium, but afterward proved, by the aid of the spectroscope, to be new.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. 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


thall(o)- (from its green spectral line) + -ium.
(American Heritage® Dictionary of the English Language, Fourth Edition)
Coined based on Ancient Greek θαλλός (thallos, "green branch") (after the color of the radiation spectra). (Wiktionary)


  • The name thallium comes from the Greek word thallios which means a green twig, which is a reference to this green line.


  • JOHN HENRY, CLINICAL TOXICOLOGIST: You could call thallium poisoning chemical torture.

    CNN Transcript Nov 20, 2006

  • Her son, Sipho, was poisoned with a rare substance called thallium, while in detention with a friend, Topsy

    ANC Daily News Briefing

  • Doctors at Groote Schuur hospital discovered he had been poisoned with a rare substance known as thallium, which left him seriously ill and confined to a wheelchair.

    African National Congress Statement to the Truth and Reconciliation Commission

  • Separated U-233 is always contaminated with traces of 232U (69 year half life but whose daughter products such as thallium-208 are strong gamma emitters with very short half lives);


  • Unfortunately the addition of lead or other heavy metals (such as thallium) makes the product very soft and also very subject to attack by gases such as are always present in the atmosphere of cities.

    A Text-Book of Precious Stones for Jewelers and the Gem-Loving Public

  • So thus we launched a broad based educational effort to highlight opportunities for providing imaging solutions to patients using alternatives, such as thallium where appropriate.

    Healthcare Sector and Stocks Analysis from Seeking Alpha

  • a 2006 paper published by other researchers in the journal Physical Review Letters, . . . suggested that elements such as thallium and tellurium could interact on a quantum-mechanical level to create a resonance between the thallium electrons and those in the host lead telluride thermoelectric material, depending on the bonds between the atoms.

    Solar power, heat engines, good stuff

  • Separated U-233 is always contaminated with traces of U-232 (69 year half life but whose daughter products such as thallium-208 are strong gamma emitters with very short half lives); the similar problems in recycling thorium itself due to highly radioactive Th-228 (an alpha emitter with two-year half life) present; some weapons proliferation risk of U-233 (if it could be separated on its own); and the technical problems (not yet satisfactorily solved) in reprocessing solid fuels.

    NEI Nuclear Notes

  • Coal waste contains heavy metals, such as mercury, lead, thallium and arsenic, which can cause birth defects and nervous - and reproductive-system disorders.

    Jeff Biggers: Pattern of Violations: Black Cross Movement Calls Out Dangerous Navajo Coal Mines (Photos)


Log in or sign up to get involved in the conversation. It's quick and easy.

  • The toxic properties of thallium compounds were recognized soon after the discovery of the element in the 19th century. Thallium compounds in toxic doses cause lack of coordination, trembling, hair loss, and finally respiratory distress, which results in death by asphyxia.

    February 27, 2015

  • Tl

    December 1, 2007