Definitions

1. noun

A soft, silvery-white, highly toxic metallic element, occurring in small amounts in some minerals and used as a poison in rat control and in some scientific applications.

“The laboratory used thallium to create a highly reactive compound for their experiment.”

2. chemistry

The chemical symbol Tl.

“The periodic table listed thallium as Tl.”

3. noun

A rat poison, especially one made from thallium sulfate.

“The farmer used thallium to control the rat infestation in his barn.”