atomic number 81
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|Noun||1.||atomic number 81 - 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|
metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.