D defs.my
Entry 1 sense Webster, 1913

Thallium

/thăl'ēəm/ · Thal·li·um · IPA /ˈθæliəm/
01 n. A rare metallic element of the aluminium group found in some minerals, as certain pyrites, and also in the lead-chamber deposit in the manu…
  1. 1.
    A rare metallic element of the aluminium group found in some minerals, as certain pyrites, and also in the lead-chamber deposit in the manufacture of sulphuric acid. It is isolated as a heavy, soft, bluish white metal, easily oxidized in moist air, but preserved by keeping under water. Symbol Tl. Atomic weight 203.7.(Chem.)