/lan"theuh neuhm/ , n. Chem.
a rare-earth, trivalent, metallic element, allied to aluminum, found in certain minerals, as monazite. Symbol: La; at. wt.: 138.91; at. no.: 57; sp. gr.: 6.15 at 20°C.
[ lanthan- ( lanthánein to escape notice; referring to its position on the periodic table) + -um, var. of -ium -IUM ]