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DictionarythalliumChemical element
noun

thallium

THAL-ee-um/ˈθæliəm/

A soft, toxic metallic element with atomic number 81.

The sealed specimen jar holds a soft piece of silvery-gray thallium.

A sealed laboratory specimen jar containing a dull silvery-gray metal piece with a deep indentation and curled shaving suggesting softness.
Etymology
thallGreekyoung shoot, green branch
+iumLatinelement-name ending

The “green branch” root refers to the green line in thallium’s spectrum, by which Crookes detected it. Adding the element-name ending turned that color image into a chemical name.

In context

Into the Shadows8:06
As we said at the start, thallium is a toxic heavy metal.
Thallium: The Perfect Poison

More examples

  • Thallium has atomic number 81 on the periodic table.
  • The laboratory tests the water for traces of thallium.
  • Because thallium is toxic, only trained staff handle the sample.

Forms

thallium