Real Dictionary

terbium in American English
a soft, silver-gray, ductile chemical element, one of the rare-earth elements, found in gadolinite and other minerals: symbol, Tb; at. no., 65
noun: a rare-earth, metallic element present in certain minerals and yielding colorless salts; at. no.: 65; at. wt.: 158.924; sp. gr.: 8.25

terbium in British English
noun: a soft malleable silvery-grey element of the lanthanide series of metals, occurring in gadolinite and monazite and used in lasers and for doping solid-state devices. Symbol: Tb; atomic no: 65; atomic wt: 158.92534; valency: 3 or 4; relative density: 8.230