a rare, poisonous, bluish-gray, soft, metallic chemical element, used in making photoelectric cells,
rat poisons, etc.: symbol, Tl; at. no. 81 see the periodic table of elements in the Reference Supplement
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'thallium'
ModL: so named by Crookes
, its discoverer < Gr thallos,
young, green shoot (< thallein:
) because of its green spectral line