thallium

noun

thal·​li·​um ˈtha-lē-əm 

: 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

Examples of thallium in a Sentence

Recent Examples on the Web

After his release, Miller started a business called Collect The Periodic Table (CTPT) and sold samples of elements such as plutonium, which is highly radioactive, and thallium, which is highly toxic, according to prosecutors. — Landon Mion, FOXNews.com, 6 Oct. 2026

Miller sold plutonium to 67 customers in the United States and abroad, and thallium to 71 customers, Foley said. — Digital Producer, CBS News, 6 Oct. 2026

That includes 1,000 tons of copper, 170 kilograms of gold, almost 2 tons of silver, over 20 tons each of bismuth and titanium, over 2 tons of palladium, and 76 kilograms of thallium. — Scott K. Johnson, ArsTechnica, 20 Aug. 2026

The agency found elevated concentrations of lead, arsenic and thallium in the soil. — Sacbee.com, 8 July 2026

Word History

Etymology

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

First Known Use

1861, in the meaning defined above

Rhymes for thallium

• allium
• gallium
• pallium

Kids Definition

thallium

noun

thal·​li·​um ˈthal-ē-əm 

: a soft poisonous metallic element that has characteristics similar to lead see element

Medical Definition

thallium

noun

thal·​li·​um ˈthal-ē-əm 

: 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