a soft, malleable, silvery chemical element, one of the rare-earth elements and the first member of the lanthanide series: symbol, La; at. no., 57
Origin of lanthanumModL: so named (1839) by G. Mosander (see erbium) ; from lanthana, lanthanum oxide, literally , the hidden one ; from Classical Greek lanthanein, to be hidden (see latent): it had previously been undetected in the mineral cerite
A soft, silvery-white, malleable, ductile, metallic rare-earth element, obtained chiefly from monazite and bastnaesite and used in glass manufacture and with other rare earths in carbon lights for movie and television studio lighting. Atomic number 57; atomic weight 138.91; melting point 920°C; boiling point 3,464°C; specific gravity 6.145 (at 25°C); valence 2, 3. See Periodic Table.
Origin of lanthanumNew Latin, from Greek lanthanein, to escape notice (from the finding of the element hidden in oxide of cerium).
From Ancient Greek λανθάνω (lanthanō, “escape notice”), because it had gone long undetected in mineral ores.