/thal"ee euhm/ , n. Chem.
a soft, malleable, rare, bluish-white metallic element: used in the manufacture of alloys and, in the form of its salts, in rodenticides. Symbol: Tl; at. wt.: 204.37; at. no.: 81; sp. gr.: 11.85 at 20°C.
[ 1860-65; thall- ( thallós green stalk) + -ium -IUM; named after green line in its spectrum ]