a silvery-white ductile metallic element of the lanthanide series, occurring principally in bastnaesite and monazite: used in pyrophoric alloys, electronic devices, and in glass manufacture. Symbol: La; atomic no: 57; atomic wt: 138.9055; valency: 3; relative density: 6.145; melting pt: 918°C; boiling pt: 3464°C
Word origin
C19: New Latin, from Greek lanthanein to lie unseen
lanthanum in American English
(ˈlænθənəm)
noun
a soft, malleable, silvery chemical element, one of the rare-earth elements and the first member of the lanthanideseries: symbol, La; at. no., 57
Word origin
ModL: so named (1839) by G. Mosander (see erbium) < lanthana, lanthanum oxide, lit., the hidden one < Gr lanthanein, to be hidden (see latent): it had previously been undetected in the mineral cerite