thallium

noun thal·li·um \ ˈtha-lē-əm \

Updated on: 2 Apr 2018

Definition of thallium

: a soft poisonous metallic element that resembles lead in physical properties, occurs sparsely in a number of common ores, and is used chiefly in the form of compounds especially in photosensitive devices and formerly as a pesticide — see Chemical Elements Table

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Recent Examples of thallium from the Web

Ash storage sites at the plant are leaking into surface water and groundwater upstream of drinking water intakes for more than 1 million people in the Charlotte region, the report says, calling the thallium and radium results alarming.

— deon roberts, charlotteobserver, "Groundwater at Duke Energy coal ash sites faulted for high radioactivity levels | Charlotte Observer," 20 Mar. 2018
There, in Islamabad, Naeem had a thallium stress test to assess the damage.

— sorayya khan, Longreads, "The Cities in Me," 8 Feb. 2018
One of Koremlu’s active ingredients was thallium acetate.

— kat eschner, Smithsonian, "Three Horrifying Pre-FDA Cosmetics," 26 June 2017
Yes, Dr. Li had specialized knowledge and access to thallium but as a Joann Curley proves, such training isn’t really necessary for a determined killer.

— deborah blum, WIRED, "The Chemist as Murderer," 23 Feb. 2011
One of Koremlu’s active ingredients was thallium acetate.

— kat eschner, Smithsonian, "Three Horrifying Pre-FDA Cosmetics," 26 June 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thallium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Origin and Etymology of thallium

New Latin, from Greek thallos green shoot; from the bright green line in its spectrum

NEW! Time Traveler

First Known Use: 1861

in the meaning defined above

See Words from the same year

Medical Dictionary

thallium

noun thal·li·um \ ˈthal-ē-əm \

medical Definition of thallium

: a sparsely but widely distributed poisonous metallic element that resembles lead in physical properties and is used chiefly in the form of compounds in photoelectric cells or as a pesticide —symbol Tl — see Chemical Elements Table