Try Our Apps


Avoid these words. Seriously.


[thal-ee-uh m] /ˈθæl i əm/
noun, Chemistry.
a soft, malleable, rare, bluish-white metallic element: used in the manufacture of alloys and, in the form of its salts, in rodenticides. Symbol: Tl; atomic weight: 204.37; atomic number: 81; specific gravity: 11.85 at 20°C.
Origin of thallium
1860-65; < New Latin, equivalent to thall- (< Greek thallós green stalk) + -ium -ium; named after green line in its spectrum Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
Cite This Source
Examples from the Web for thallium
Historical Examples
  • We will now remove the thallium and put a bit of silver in its place.

    Six Lectures on Light John Tyndall
  • The simplest curve of this type will be obtained when only one compound is formed, as is the case with mercury and thallium.

  • The thallium papers show that the greatest effect is in the daytime, the iodide papers that it is at night.

  • The iodide curve follows closely that of relative humidity, clouds, and rain; the thallium curve stands in no relation to it.

  • They are not absolutely insoluble in water, and the sulphide of thallium being brown, would probably be damaged by impure air.

    Field's Chromatography George Field
  • That thallium affects the colour is most probable, but it is not necessarily the cause of the orange hue.

    Field's Chromatography George Field
  • On chromate of cadmium, made with bichromate of potash, thallium would naturally confer an orange hue.

    Field's Chromatography George Field
  • thallium is a widely-diffused metal, being found in many minerals, particularly in iron- and copper-pyrites and native sulphur.

  • The spectrum of thallium consists of a single most characteristic line of a beautiful green colour.

  • Copper, alloyed with only one half per cent, of thallium, becomes quite brittle; but the alloy with tin is malleable.

British Dictionary definitions for thallium


a soft malleable highly toxic white metallic element used as a rodent and insect poison and in low-melting glass. Its compounds are used as infrared detectors and in photoelectric cells. Symbol: Tl; atomic no: 81; atomic wt: 204.3833; valency: 1 or 3; relative density: 11.85; melting pt: 304°C; boiling pt: 1473±10°C
Word Origin
C19: from New Latin, from Greek thallos a green shoot; referring to the green line in its spectrum
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Cite This Source
Word Origin and History for thallium

rare metallic element, 1861, Modern Latin, from Greek thallos "young shoot, green branch" (see thallus) + element name ending -ium. So called by its discoverer, Sir William Crookes (1832-1919), from the green line in its spectrum by which he detected it.

Online Etymology Dictionary, © 2010 Douglas Harper
Cite This Source
thallium in Medicine

thallium thal·li·um (thāl'ē-əm)
Symbol Tl
A soft, malleable, highly toxic metallic element, used in photocells, infrared detectors, and low-melting glass. Atomic number 81; atomic weight 204.38; melting point 303.5°C; boiling point 1,473°C; specific gravity 11.85; valence 1, 3.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
Cite This Source
thallium in Science
Symbol Tl
A soft, malleable, very poisonous metallic element that is used in photography, in making low-melting and highly refractive glass, and in treating skin infections. 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 Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
Cite This Source

Word of the Day

Nearby words for thallium

Difficulty index for thallium

Some English speakers likely know this word

Word Value for thallium

Scrabble Words With Friends