Definition of Thallium 1. A soft grey malleable metallic element that resembles tin but discolors on exposure to air; it is highly toxic and is used in rodent and insect poisons; occurs in zinc blende and some iron ores Noun Synonyms for word "thallium" Semanticaly linked words with "thallium" Hyponims for word "thallium" etymology nonthallium etymology organothallium etymology radiothallium etymology thalliferous etymology talium etymologically related thallate etymological origin of θαλλός is derived from eka-thallium is derived from thall- is derived from thallane is derived from thallic is derived from thalliferous is derived from thallious is derived from thallium glass is derived from thallium green is derived from thallium hydroxide is derived from thallium line is derived from thallium monofluoride is derived from thallium monoxide is derived from thallium oxide is derived from thallium sulfate is derived from thallium sulfide is derived from thallium sulphate is derived from thallium sulphide is derived from thallium trioxide is derived from thallium-activated is derived from thallo- is derived from thallous