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
See lanthanum in American Heritage Dictionary 4
(lănˈthə-nəm)
noun Symbol La
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 3,469°C; specific gravity 5.98 to 6.186; valence 3. See Table at element.