Longman Dictionary of Contemporary English homepage

Date: 1800-1900
Language: Modern Latin
Origin: Greek thallos 'new green plant part'; because it has a bright green line in its spectrum

thallium

 noun
     
thal‧li‧um [uncountable]
a soft blue-white metal that is poisonous, used in photoelectric cells and to kill rats, mice, and insects. It is a chemical element: symbol Tl
Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.

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