Thăl'li-ŭm, n.

n. [Gr. θαλλός, young shoot or branch, twig.] (Chem.) An alkaline metal closely resembling lead in general appearance, being of nearly the same color, density, and softness, but in its chemical relations similar to the alkali-metals potassium and sodium; — so called from the bright green line which it gives in the spectrum analysis, by means of which it was discovered by W. Crookes, of London, in 1861.