Definition of "thallium" [thal•li•um]

• A soft, malleable, highly toxic metallic element, used in photocells, infrared detectors, low-melting glass, and formerly in rodent and ant poisons. Atomic number 81; atomic weight 204.38; melting point 303.5°C; boiling point 1,457°C; specific gravity 11.85; valence 1, 3. See Table at element. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The name thallium comes from the Greek word thallios which means a green twig, which is a reference to this green line."
• "JOHN HENRY, CLINICAL TOXICOLOGIST: You could call thallium poisoning chemical torture."
• "Her son, Sipho, was poisoned with a rare substance called thallium, while in detention with a friend, Topsy"