a malleable ductile silvery-grey element occurring principally in monazite. The radioisotope thulium-170 is used as an electron source in portable X-ray units. Symbol: Tm; atomic no: 69; atomic wt: 168.93421; valency: 3; relative density: 9.321; melting pt: 1545°C; boiling pt: 1950°C
Word origin
C19: New Latin, from Thule + -ium
thulium in American English
(ˈθuliəm; ˈθjuliəm)
noun
a bright, silvery chemical element, one of the rare-earth elements: symbol, Tm; at. no., 69
Word origin
ModL: so named (1886) by L. de Boisbaudran (see gadolinium) < thulia (from which it was isolated by Cleve in 1879) + -ium