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
Substances used most include antifreeze, eye drops containing tetrahydrozoline, fentanyl, cyanide, thallium, colchicine, veterinary barbiturates and insulin.
—
Emma Bussey , Alexandra Koch, FOXNews.com, 5 Feb. 2026
Substances most often used in domestic poisoning incidents are antifreeze, eye drops, the synthetic opioid fentanyl and the prescription medication colchicine, as well as cyanide and the chemical element thallium, according to the note.
—Aaron Katersky, ABC News, 3 Feb. 2026
The girls died in April after allegedly ingesting raspberries contaminated with thallium, a highly dangerous and odorless metal, the publication reported.
—Becca Longmire, PEOPLE, 18 Dec. 2025
According to the complaint, Hanmer watched a video on how to create thallium sulfate on April 5 and May 15.
—Trent Abrego, Twin Cities, 6 Sep. 2025
See All Example Sentences for thallium
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Emma Bussey , Alexandra Koch, FOXNews.com, 5 Feb. 2026
Substances most often used in domestic poisoning incidents are antifreeze, eye drops, the synthetic opioid fentanyl and the prescription medication colchicine, as well as cyanide and the chemical element thallium, according to the note.
—Aaron Katersky, ABC News, 3 Feb. 2026
The girls died in April after allegedly ingesting raspberries contaminated with thallium, a highly dangerous and odorless metal, the publication reported.
—Becca Longmire, PEOPLE, 18 Dec. 2025
According to the complaint, Hanmer watched a video on how to create thallium sulfate on April 5 and May 15.
—Trent Abrego, Twin Cities, 6 Sep. 2025
See All Example Sentences for thallium
Cite this Entry
“Thallium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/thallium. Accessed 16 Feb. 2026.
Copy CitationKids 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
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